I honestly think that this suggestion would answer most people's requests here. By this point in the game's lifespan, I'd say that full modding tools are unlikely to damage DLC sales, but instead bring new life into the game as people may even be incentivized to buy the game just to play some of the new mods that will pop up (like a fully remade Blitzkrieg mod in the form of Spearhead mod). I personally for example, would like to play with a lot of historically accurate units that would never make it into vanilla and it's perfectly fine that they don't. Things like the SU-122, Marder III, Hungarian infantry, etc. These units, new factions, new abilities could all be added with full modding controls. Better still, Relic need only release the tools and the community will do all of the work.
To this day, many people still play vCoH, even with all the mods available. In a similar way, it's unlikely that people will drop vanilla CoH 2 just for mods. Post opinions below.