I think a big problem you'll hit here is that a large number of gamers are generalists - we enjoy playing a variety of games and have a variety of skills accumulated from that experience. That means that the FPS portions of the game are either going to match our challenge level and discourage factory builder specialists or it's going to be extremely underwhelming for FPS players. Factory builder specialists - those folks who absolutely adore DSP and Factorio but who, when dealing with the threats in Factorio, leverage creeping turret walls and artillery to clear the creep and who try and avoid fighting on foot outside of the very earliest game stages.

Building multi-genre games is a really hard problem.