We actually participated in a hospex summit this year and discussed this very thing with leaders from BeWelcome and Trustroots. You can watch the whole thing on youtube 
@Nolo @aapeli and I all spoke at some panels.
This is the thread that pertains to it - HospEx Summit
However, despite the great conversations and topics that were covered, none of us got the impression that we can work together to the extent you suggest; all of us have very different agendas and visions for what the future should look like, and it was generally agreed that having different options is a good thing. There’s room for everyone running a non-profit, in my opinion.