Ideas

Add editor only Palisade Walls (short, long, etc) based on the standard wooden walls with an exclusive WallBuild2 flag that can be used by modders to re-add Palisades, or similar walls.

Essentially a port over of the Kallanka ability from AoE3, basically reduce the population of units contained within the building, and allow it to be exposed to the techtree.

Port over (or add a similar trigger based on Render Snow) the Render Rain(percent) trigger from Age of Empires 3 so modders don't have to place Ra Rain actors everywhere.

Similar to the "Resources last x% longer" bonus from Age of Empires II, ResourceYield (or something similarly named) was added into Age of Empires III: DE, and allows for gatherers to gather more from resources (i.e Gold Mines) whilst taking less from the mine itself.

This feature would also be exposed to the Techtree, where it would find the most use amongst modde

Add a new unit property for impact data, that allows for an unit (typically a projectile) to spawn a splash object upon colliding with a unit's obstruction radius.

This property would be useful for representing explosives, such as grenades.

Expose ranged unit's accuracy, spread factor and max spread variables so that they can be modified by the Techtree files for use in technologies that can improve ranged unit accuracy.

Furthermore Building's BuildingWorkRate, which affects how a fast a protounit building can train, and research should also be exposed for modification by the techtree.

Currently as of AoMEX, there is no way to transform a unit without pressing the transform button, which makes it so custom siege weapons in the vein of the Trebuchet from AoE2 have to manually transform to be useable.

This could be circumvented by the addition of a UnitTransformOnAttack and UnitTransformOnMove protounit flags that allow for a unit to automatically transform on attack, and when moving respectively.

As of AoMEx, when adding Farm-type buildings (i.e Fish Traps, Plantations/Flax Fields, Forestries, etc) when a builder is finished building these gatherable buildings, they will either idle or attempt to build nearby unfinished buildings instead of gathering, likely due to builders being preprogrammed within the source code to only attempt gathering from Farms when completing them.

BuilderGathersAutomaticallyWhenCompleted or another similarly named flag would be used by the gatherable building to tell it's builder to gather from it upon it being completed, and would takeover the source codes role direct role in this matter.

Add two new config strings that control the maximum amount of rows and columns the Command Panel can utilize for techs, units and abilities.

Currently as of AoMEX, the maximum amount of rows that can be used are 3, with the maximum amount of columns being 8. Without uimain.xml modding, the standard amount of columns and rows shown are 3x7, though the engine can support an additional column at the moment with modding.

Expand AreaAttack param flags by adding in two new flags that allow the action to be suitable for Trample Damage (i.e dealing area of attack when moving)

These flags should be "WhenMoving" and "WhenAlive" the former tracks when the unit is moving, enables the action, whilst the latter enables the action when the unit's hitpoints are above 0.

Team game strategies could be more interesting if you could choose who is pocket vs who is on the edges

to be able to download the recx of all players as in voobly

On multiplayer if too many sounds play at once the game glitches out and stops playing sounds of certain types. Over time this causes many sounds to go missing until the game is restarted. This carries between games.
This is a request to investigate and fix the bug.
An easy way to reproduce is to cast chicken storm god power in multiplayer which usually triggers it. Also just large battles will also do it.

My actual preference is to remove autoqueue completely, however, I realize that this is an unpopular opinion with many current players. Therefore, I think that we could compromise! Remove autoqueue from ranked games 🙂, so any casual or non-ranked (community) games can include autoqueue.
Hear me out: (the following are my main points)
Autoqueue does not exist in other notable RTS games (including other "Age of " games) - it only exists in one or two other small games. If we want to attract more players, I think that autoqueue would be more of a detriment than a benefit.
  Multitasking is a skill that should be rewarded in competitive play. Handling army, economy, defense, and offense all at the same time is a LOT easier when you don't need to focus on creating units. 
  I think that autoqueue is too similar to "the game playing itself". I don't think that it is simply automating repetitious actions.
  AoM has a good balance of manual mechanics and "ease of life" mechanics. For example, with building groups and hotkeys, you can easily queue up many units at one time with 2 keyboard strokes. A bad example of manual mechanics is AoE1 & [original] AoE2 -> farms had a limited amount of food, so the player was required to rebuild a farm when the food expired. Farms are a non-issue in AoM, but I think that this is a bad example of manual mechanics - later in the game, you would be required to rebuild 30-60 farms again and again and again. A good example of manual mechanics is the necessity to create which units you want to use.
  Compare AoM to chess. Many top chess players become bored with chess because chess engines can play almost perfectly. This leads to human players memorizing engine-generated moves instead of using their own brain power and creativity. I think that autoqueue is a little bit like this - it adds in a technological aspect that, in a way, removes the humanity and human creativity from the game. This thought again relates to the idea of "the game playing itself". Humans make mistakes, and that makes the game more dynamic and impressive when you see a top-level player who truly plays the game so incredibly well.  Ultimately, I want AoM to be as popular as AoE2! I want to see tournaments and mods and scenarios and YouTube videos and sponsorships and everything! I think that to do this, we need to assess what would make the game more enticing to both casual and competitive players. I think that keeping autoqueue is a detriment, but we could compromise and only remove autoqueue from ranked games.

When triggers stop working there should be a message popup that helps you figure out where the problem comes from.

The current render sky trigger effect only allows the author to specify a path of one the four existing skyboxes in the game or have them create their own sky. More skies to choose from or the ability to override an icon instead would be most welcome.

A new trigger effect that would apply a texture mask to the selected unit, for example frost or bronze (these are actual icons, so maybe an even better suggestion is to let the author freetext an icon path) and then specify time before reverting to default.

Currently custom scenarios all share the same icon. Perhaps there could be the ability for the author to specify the icon path to represent their scenario when it is hosted in  MP lobbies?

Currently the change name trigger does not work in custom made Random Map Scripts, please allow this.

Oftentimes when hosting a custom map, we need certain players to be CPU. Usually it would be something like "last player MUST be CPU!" or "last 2 players MUST be CPU!"
We would like a feature that allows us to add hidden players to our custom maps that do not show up as available slots in the pre-game lobby or are already filled with computers.
Alternatively, add a function that allows us to add a computer player on game startup, which can achieve the same result.

Give each team a few vetos against the map pool  - the maps not vetoed by either side are are the pool for the match. In teams, the party boss chooses them.

Disable titans, and use the DM map set as defaults, and ensure that the mode doesn't spawn relics that don't affect it (upgrade cost reductions).

It would be hugely useful for content creators and tournaments to make scenarios more accessible to cover with replays and spectator mode

A small number of properties for a unit can be changed via modify protounit trigger and some techs but otherwise unit modifications are not possible.
It would be nice to expand to provide full API for editing all unit properties listed in there (Other than critical ones such as object name, unit type) which would include:
* Adding/Modifying/Removing properties such as obstruction radius, bounty factor, turn rate, decay time.
* Adding or removing the many supported flags.
* Adding/Modifying/Removing action types. E.g. Change the attack on some special attacks, or the radius or splash attacks, Add or remove regen persistent actions, even silly things like have minotaurs gore units across the map etc.
* Other property changes such as changing what units can be trained, changing what techs can be researched, allowing other units to carry relics, etc.
The possibilities this would provide for scenario designers for custom games is enormous!
Maybe the simplest way to enable it would be to allow an xml fragment to be accepted for a unit id/name and it overrides the protounit data with the provided fragment but there are probably neater ways.

A very large number of maps use god powers that are modified with triggers to have a completely different effect to what the game originally had them do. However it is difficult to convey a powers function when you cannot change it's icon to another texture. This is to allow a trigger to set the icon for a displayed god power slot to a new one via triggers.
Note if the larger feature request of allowing lobby transfer and immediate play somehow makes it in then this may become obsolete.