Yes, I'm aware of Stormgate.
I'm gonna tell you something that I'm afraid is gonna get ignored. 99% of the problems of SC2 Coop is from allies who are bad players (bad as in incompetent, and bad as in uncooperative or egotistical). I know Stormgate is aiming to be a "social RTS" and that's a big part of your marketing strategy, but could you please make the coop mode "Up to 3P" instead of "just 3P"? So that it can have 3 players, 2 players or just 1 player. In that last one, the mode would be a single-player Comp Stomp mode, but with the same maps, over-the-top factions and units as co-op. In terms of game design, it's relatively easy. You can design and balance the missions of the mode for 3P, and scale down objectives (in numbers and/or hitpoints) and enemies the fewer players there are, so the fewer players are not overwhelmed by what needs to be done.
Barring that, if you still go for only-3P coop mode, as opposed to "Up to 3P Comp Stomp" mode, then can you at least design it in such a way that griefers, teamkillers, weak/incompetent players, AFKs, etc. have little or no negative effect on the remaining players? From a game design standpoint, that seems to be a lot more complex to me than my previous suggestion. Sure, you can make it so only 1 player is needed to capture locks on "Lock and Load", but how do you scale down the difficulty dynamically, after the match has started, if a player isn't holding his own on his half of the map and is constantly getting wrecked by enemy waves and constantly needs to be rescued by his ally?
Please do not reject my idea out of hand and kindly let the rest of the team know that there is interest in a single-player comp stomp mode.
BTW, I just watched the infernal faction reveal. Looking good!
Last but not least, thank you, to you and the whole team, for your hard work and your contributions to the RTS genre. I hope Frost Giant and Stormgate do well. :)