It is relatively absurd how little can be added to an asset pack. Archives that do not meet the stringent structure requirements are ignored by the game. Custom sounds and 3D models for scenarios asset packs are not even a remote possibility without unsanctioned reverse engineering.
The reasoning behind this decision is likely based on security for the player and the brand; players are prevented from downloading anything outside of the realm of what should be expected from a mod, and Relic/SEGA do not have to worry about content creators designing entire factions for their scenarios, which would eventually threaten the appeal of DLC. I get it, believe me — I've worked with Paradox games for many years.
I am being somewhat facetious, of course. Both reasons are understandable.
But regarding the latter, I would like to request some reconsideration. Company of Heroes 2 is an eight year old game, for which the latest fully-featured DLC released more than six years ago. Correct me if I'm wrong, but I do not think there will be any more DLC for this game. It's very clearly on long-term support, which is fine, but if the official developers are done releasing new content, consider loosening these draconian restrictions on what the community can make themselves.
To be clear, I am certainly not asking for source code of the game. But I do not believe it would be unfair to request the Archive Structure whitelist for Asset Packs to wildcard include any subpath and filetype found in "Art" or "Sounds" archives from the base game, with the reasonable exception of .lua or .csv files. The official tools used to compile and decompile "Relic Chunky" formats for sounds/models and their companion files would be appreciated as well.
I hope this post somehow makes it to the eyes of someone who can consider the potential benefit from a business perspective. It is not too late for a fresh wave of community content to revitalize interest in the game. It would have a much stronger pull than free weekends on Steam. I appreciate your time regardless.