Like others have said in this thread, I think one of the main reasons MS is buying out these studios is to start A-AA level content creation to their gamepass. Kind of like Netflix does, produce content to your monthly subscriber base.
Buying Relic would make things interesting, as they're primarily a PC developer. Microsoft adding full-blown keyboard and mouse support to their Xbox consoles could indicate that they intend the gamepass and its games to be fully playable on all systems which supports the gamepass or Xbox Live ecosystem. You could switch seamlessly between your PC, Xbox and probably in the future, systems X and Y.
This really would be an interesting take on the "Netflix of video games" idea that Google with Stadia seems to be also aiming for.