« and soon Diaspora are part of this same network [ie. ActivityPub] » — I was surprised to read that, and after a quick check, it's not looking like it'll happen anytime soon, sadly.

diaspora* is one of the most famous and successful open, federated social networks out there, yet it does not implement the protocol which is gaining unprecedented traction across a large number of implementations. Hopefully, Nextcloud implementing ActivityPub is yet another reason for diaspora* to follow the move.