TBH, at this point I would take anything and plenty of write-ups have been done to show what GSC units could work for which roles and all that.
But I would prefer a faction that is on the side of our enemies. I saw the whole opposed enemy faction thing in AFTE and it was neat the first few times, sure, but, in the end, it just kinda slows everything down and takes the pressure off the players which, for a game like this, is just kinda anti-fun. People already complain endlessly about smite. Imagine if every time the two factions were on screen they’d just ignore the players and shoot each other while you lazily line up headshots. The devs have done well with the baddie AI in this game and could probably come up with something a little more engaging than that, but any way you figure it, it’d still take heat off the players.
I’d also like to avoid the Soulstorm-levels of plot contrivances it takes to get all the various factions brawling over one forsaken and crapped-on little system. So far we’ve had a coordinated uprising paired with an attempted military coup all orchestrated by the followers of one chaos god. They have two readily-available allies near at hand in the setting that’s been established: the infinite hordes of daemons that can be summoned once the division between the Material and the Warp becomes thin, and the unknown xenos from Nox Alpha who are believed to have been involved in the corruption of the Moebian 6th. The “Noxians” are particularly a threat as they have burst forth from their final hold-out on Nox Alpha just as the Domain recalled many of their forward deployed troops. They have retaken multiple systems setting back the progress of the Fringe War by thousands of years and contact has even been lost with the heavily-fortified Naval garrison-world of Komaris. Their forces are believed to be within striking distance of the Atoman system so it would make sense for them to exploit the beachhead their human quislings have established for them and make an appearance.
I guess I like the idea of that logical progression rather than “unbeknownst to all, the fighting has triggered the defense instincts of the local Genestealer cult’s broodlord who has now sent his minions forth” and then “unbeknownst to all, a wandering Ork Waaagh happens into the system and thinks it looks like a fun fight” and then “unbeknownst to all, the Dark Eldar decide that now is an excellent time to raid some slaves for their villainous and hedonistic designs” and then “unbeknownst to all, an Elkdar Farseer has had a vision that the outcome of the Battle for Tertium may well decide the fate of the entire Eldar race and has dispatched all forces” and then “unbeknownst to all, Atoma Prime was secretly a Necron tomb world this WHOLE TIME! dun dun duuuh . . .” and then " . . . " and then " . . . ", etc.
Know what I mean?