Reminds me of Warcraft 3. The last expansion came out in 2003, and the mod community was still going strong into at least the late 2000s when I was still playing.
I used to be one of those people reverse-engineering Red Alert 2, and those years were certainly fun and challenging, as well as illuminating in the "this is why you don't <bad coding practice>" sense.
Fun fact: When EA repackaged those old C&C games for The First Decade bundle, they removed the No-CD checks. Most of the games were recompiled to achieve that, but since Red Alert 2 had these engine patches relying on absolute addresses, they went through the trouble of hex-editing the executable to keep the patches working.
But please spare us from a console first RTS game like Halo Wars. This dumbed down gameplay is a joke compared to real RTS game genre. It's all about controlling many individual units over a huge map, building building wherever one things it makes sense, gathering several types of resources, managing a economy, scale everything, defend from smart AI enemies, conquer enemy bases, play on random generated maps against AI enemies, etc. Halo Wars and Command and Conquer 4 were the worst breed of RTS games, console first games with casual gameplay, very limited base building on predefined spots, limited units, slow gameplay, narrow field of view, smaller maps. Basically everything worse than what PC gamers were used to with previous RTS games. This cancerish development destroyed the RTS genre - and since 2005 (beside SC2) no triple A RTS worth mentioning got released. No "new real" Age of Empires/Mythology, Empire Earth, Command and Conquer. E-sport focused SC2 got several low budget RTS clone games in futuristic settings, and strategy fans in general got several games outside of the true classic RTS genre, but they are different in style in many ways. Also tower defense and Moba originated from RTS from mods of Age of Empires 1/2 and WarCraft 3, and got several clone games, but have little in common with the true RTS game - no free base building, no resource gathering. "Modern games" are simply too much casual gameplay, too much grinding mechanic, just a few units, no strategic planing, no micro+macro management of hundreds of units over a 2hour timespan. It's more like true RTS games are for educated people loving grand scheme of strategy and historic war strategy to try out new things, and "modern games" cater only the Free2Play crowd that never experienced good games, are more about simple gameplay with a lot of repetition and casino tricks to get the crowd addicted plus a few gamification tricks, random generators with in game stores to buy cards. wtf have cards you should buy with real money to do in an RTS game during real time strategy action - ask those who brought you Halo Wars 2, the latest trainwreck. Nowadays there is 0 A.D. an open source RTS like AoE and the possibility to play decade old RTS games - but it's boring as well. No cheap "HD" remakes will "reboot" RTS games, only real new classic RTS games with good old mechanics and PC first development can surface good games. And console gameplay is possible, e.g. WatchDogs2 has complex controls to steer a drone in 3D space and controlling physical objects in a RTS style fashion all while playing a 3D character - so innovation is possible, and WD2 is basically a possible way forward. Beside that WD2 is also the better Deus Ex game, having all the things that made Deus Ex 1 so great, and non of the later Deus Ex parts achieved. WD2 is also very funny and plays in SF ad the valley, it's a persiflage, and a superb game.
Even Warcraft 2 is still being played - check out https://www.youtube.com/user/war2combat which is truly amazing!
Warcraft 3 is alive and well, which makes me incredibly happy.
And I think this ties in with the Mod theme of the title very strongly. I don't _love_ RTS games, I can play them but it's not my biggest hit. But the Warcraft III custom games simply blew me away. As a teenager with a fairly limited game budget I have gotten a ludicrous amount of enjoyment out of the countless hours I've put into Warcraft III.
I'd be surprised if you told me I've played the RTS/classical mode of the game over 30 hours over my life. But if you told me I've played over 4000 hours in custom games I wouldn't even bat an eyelid.
Heck, as I said even nowadays I still reinstall and play a couple of fun maps every now and then.
I guess what I'm trying to get at is that modding support is an extremely positive thing, and derivations of your creation can truly breed a life of their own which I can only see as positive for your consumers.
Warcraft 3 custom games is probably the most influential game engine/custome game system ever created.
War3 has produced multiple genres, including MOBAs (dota, lol, etc), and freaking TOWER DEFENSE.
I play custom games on starcraft 2 every day.
The fact that there are still communities around these games kind of goes to show that modern variants of their gameplay can be overvalued. I haven't bought a new game in years because classic titles hold up so well and I still get a ton of enjoyment out of them as an adult with limited time on my hands.