I have always liked Bastions look.
Uterine does not do a lot of team ups. Although there was a what if when he got with the X danger room AI
this reminds me of the team up in Marvel vs Capcom: Infinite
Messiah Wars Bastion merging with Ultron would be really bad news, that version of Bastion was one of the X-Men's biggest threats of all time. I'd go even further and imagine that Bastion merging with Phalanx Ultron from Annihilation Conquest.
What others said it would start with them going "yes this will work and we will work together to the end" but become "wait what do you mean you don't like my end game" or they compromise and kill off like 90% of all non mechanical beings and split up the rest and do with them as they see fit? Also maybe throw in other Techie villains/beings and make a group of Techie heroes from the different Marvel corners to stop them.