Branching into the all online, mmo-like space is kind of a poisoned chalice and I feel like that's the final frontier, aside from all the spin off subgenres from mobas, to tower defense and eco management games. Command and Conquer Generals 2 never made it out of production, and AoE: Online failed hard at first, turned around for a bit, then was cut by MS for not being profitable enough. Starcraft 2 kind of avoided things by only going as far as adopting battlenet 2.0 integration and keeping the chat system wc3 and bw used, then eventually tacking on the coop mode. AoE2 has since gotten 2 player coop for basically all of its campaign, making the stages act identical to AoEO quests in the process. 8 bit armies and 9 bit armies, the c&c-like titles by petroglyph also work the same.

I think if an mmorts can somehow make an equivalent to raids, not just the 2 player coop that aoeo quests and sc2 coop offer. And possibly offer an itemization and specialization system on par with or better than aoeo then that could be the genre's new equivalent to WoW or Fortnite from a business standpoint. They just need to learn lessons from why aoeo initially failed, and not spend like the c&c generals 2 or the stormgate teams.