All the RTS games are underplayed nowadays. Starcraft 2 is maybe the most active still and has been all but abandoned by Blizzard.
A good RTS has an extremely harsh learning curve and is not super monetizable. Someone would have to rethink the genre: make it easier for casual players and figure out how to get the addicting money making patterns in. Otherwise big companies are gonna have no interest.
Sucks, I love Starcraft 2, but it is legitimately the most mentally demanding game I have ever played. Sometimes I procrastinate getting into a match because 1v1 is so stressful. I totally get why it has limited appeal.
World in Conflict was an interesting take on making RTS easier for casuals. Basically took the resource gathering part out of it. You got a constant drip of points you could spend on units instead.
Potentially that simplification hurts the genre too much though because then you don't have hardcore players sticking with it for years and years.
Maybe a game could have that as a "simple mode" that players can opt in to.
The potential addictive money making pattern is the same as other games imo. Skins. The units being smaller mean the developer is probably going to have to go to more effort to shove them in to peoples faces. Maybe a screen before/after the match where all the players units in their skins can be clear seen in a more zoomed in manner. Have them marching around the border of the end scoresheet or doing a little dance while waiting for players to load.
Perhaps a more 'casual' in the RTS genre, but AoE2 is still going very strong.
I think the problem is simply that for a large part of the playerbase, increasing your APM is directly correlated with increasing your win rate/ranking.
And frankly, that's not fun for a lot of people.
I don't want to win by clicking and mashing hotkeys like a schizophrenic on speed.
StarCraft I still has a large community. And China has a giant WarCraft III community.
Every time someone tries to re-think the genre they make it worse. Supreme Commander (and Forged Alliance) were near-perfect games, but SupCom 2 tried to simpify the game to appeal to console players and ruined it completely. Dawn of War 2, although not to everyone's taste, was in my view the peak of the series. For the third install they tried to simplify the game and bring it closer to a MOBA and it was an incredible flop.
In my view, if a develop MUST make the game more accessible, they should do so with alternate modes while still maintaining a strong competitive 1v1, 2v2 and 4v4 mode with the steep learning curve and competitive nature. Anything else is a betrayal of the genre.
The spiritual successor of Starcraft is Stormgate. I cannot comment on it, I have no idea how good it is. AFAIK it is multiplayer only. I played Dune II, Warcraft II, C&C, Red Alert, Starcraft (didn't like, I never understood the hype), Dark Reign, Total Annihilation, Warcraft III as kid, but... only single player (at various difficulties). That is just how games were generally played in the 90s. I do remember using a null modem cable at some point, but IIRC was only to play Doom and Duke3d.
I believe the RTS genre at a whole got superseded by the MOBA genre (with DotA and LoL). A genre I tried once (HotS) and was terrible at. If you're shit and you're not improving (I didn't enjoy it either, I felt forced to do it for a reward in another game), stop trying. I never tried any other MOBA, except maybe a touchscreen one, Warcraft Rumble? Either way, I got burned by Hearthstone Mercs and fell once more in the trap with Rumble. After Blizzard announced removed of addons from combat, I've finally said goodbye to the Warcraft franchise and Blizzard in general.
There's one game I really do like which has a kind of RTS with map feeling to it: Total War: Warhammer series (though I laud their BS with DLCs and multiple game versions). I suppose the whole Total War series is as good, I just like the Warhammer universe. The other day, Settlers II was discussed on here, including a FOSS clone. Settlers II is also a game I liked (III not so much though artwork was nice, never played the orig.). Supposedly it isn't RTS, tho I am pretty sure back then it was called RTS.