The fact that sounds (attack and move) are shared by lot of different units is a real and major obstacle in modding work, we can never do what we plane to do with the game because we can not choice for each unit the sound move and the attack sound we want to use.
Example : If I want to have in a mod motorized arty and no motorized arty, I can not. Why ? Because these 2 arty will share the same move sound (artillery move).
And if a mod has lot of unit types, it's impossible to manage correctly sounds
What you could do, in my opinion : To sell a little DLC that allow in editor to choice between :
* to keep actual hard coded sounds
In this case, in campaign data windows, a little box would be checked (this case would be pre-checked by default, to allow retro-compatibility with old mods and old campaigns) => nothing would be change in the actual sound system
* to choice free sounds : in this case, user could uncheck the first case and check a second case named "free sounds"
If he would have choiced "free sound", user would find that in Country data/Combat target data windows :
He could choice (for each unit) the number code of sound he want to have for each unit (one choice for move sound, one choice for attack move). Or more simple, these 2 menus (move and attack) could display names of ogg files and user would simply choice in the list the name of the ogg file he want to use for the concerned unit
(if he would have choiced to keep "vanilla hard coded sounds", option about move sounds and sounds attack would simply stay "grey inactive" in combat target data windows)
By this way, you would have no any problem of retro compatibility with old campaigns and old mods, because the "keep actual hard coded sound" box would be pre-checked. But users could choice the "sound liberty", and it would be a MAJOR improvement for the game.
I like modding SC, but I have to say that I am sometime discouraged in my work, due to the bad hard coded sound system that heavy blocks all possibilities. Why did you give a so efficient editor to users and in the same time a so bad hard coded sound system ? It is completely contradictory.
In economic terms, you could sell this DLC 12 or 14 $ : player who don't want to buy it could continue with the vanilla hard coded sounds, and player who want to have it would buy it ; no any problem of retro-compatibility would occur because the "keep vanilla hard coded sounds" box would be pre-checked in the DLC editor : without any action by user on this pre-checked case, the DLC Editor would stay 100 % full compatible with old campaigns and old mods.
I would be able to pay twice the price of SC to have this kind of sound system…
In economic terms, I think you would sell this DL without any difficulty. Why ? Because all modders would want in the futur to create their mod with "sound liberty". And as consequence, players would have to buy the "free sound DLC" to be able to play these interesting new mods made with the "sound liberty", ...
If you are afraid by the idea to sell this DLC, because tyou think is too expansive for this kind of DLC, perhaps could you consider to include in this DLC the choice of target type ("hard" or "soft") for each unit (using the same kind of optionnal choice with check boxes)...
And in addition, using same optionnal system, the choice (for each unit) of the line (line of icon counters) in unit sprites bitmaps would be also interesting.
(example : actually, HQ use line N°1 of each unit sprite in bitmaps. You could give to user the possibility to choice the line he prefers in unit sprites bitmap file : N°1, N°2, N°3 etc). By default, to preserve retro-compatibility with old mods and old campaigns, the pre-checked choice for each unit would be his actual vanilla line (Line N°1 for HQ, etc)
So, the price of the "EDITOR DLC" would be twice justified
You could rename this DLC : "IMPROVED EDITOR DLC"
And you could also include in this "IMPROVED EDITOR DLC" the project about you think here :
https://forums.matrixgames.com/viewtopic.php?t=418665
(to introduce possibility to give combat bonus or penalty for when a unit specifically targets a hexagon type, terrain or resource)
In my opinion, you could open a "public consultation" of users (essentially modders), to collect what they want to see changed or improved in editor. After examining what may be done and what may no be done, in perspective to preseve retro-compatibility, you could include these modification in the "improved editor DLC".
This DLC would not need to include new campaigns, it would just be a "technical" DLC. Considering the time of work and the great disponibility of your team for users, to have to pay for this DLC would not be problematic : SC is a great game and it's a normal thing to pay something for improvements.