I don't think thats the way Blizzard is structured. Your job is tied to a project. So you're a "Starcraft2 engine developer" you only work on Starcraft2's engine. Not Overwatch's and not Diablo. Starcraft. I don't think there is a concept of a generic "Engine Developer." How they form teams once a new idea is pitched I'm not sure but I assume they just move the "Starcraft2 engine developer" to "Overwatch engine developer."I wouldn't be surprised if they have a bunch of eager small teams pitching ideas using their bigger IPs.