I hope Spencer will remain the head of Xbox at least for this entire generation, so next 5-6 years - his plans have been put in motion, great, but it still needs time before it all starts coming together and seriously snowballing.
Right now it feels to me that XB tries to be a bit everywhere - a bit of streaming, a bit of monthly service, a bit of traditional model, PC market, mobile devices etc., it seems like they're trying to attach/gain people from here and there rather than really having that one, unified ecosystem with gamers at the center...
Because I really don't feel all those people from all those different devices belong to the same "family", even when I play games from GP on PC I don't feel those games have anything to do with XB at all, it's actually sort of a "detached" experience, where it doesn't feel that you belong to the XB, but it's not a typical Steam experience either.
So yeah, IMO Spencer should leave not earlier than when XB as a brand builds this sort of presence, when it doesn't matter where you play, you are all playing together.