Erlang and Wave
It is interesting to notice that one of the major Jabber servers is written in Erlang, and that Google Wave is a set of extensions built on top of XMPP. So, it might be very possible to build a Google Wave server on top of Erlang pretty soon.
As for Google Wave trying to do everything altogether, I don't quite agree.
I think XMPP has the potential to do all these things. Look at the laconica software for example, an open-source clone of Twitter, which powers identi.ca and floss.pro among others, and is based on XMPP. Online messaging is made of many software not because it is a requirement, but because of historical reasons : email was not an instant protocol, so IM protocols were built apart ; IM protocols (apart from XMPP, which came later) were not centralized or federated, so new protocols were created for social networks ; communication over IM protocols did not allow documents collaboration, so wikis were created. Of course, this is really schematic, but my point is that all these things are separated not because they need to, but because they came one after the other, and the existing protocols didn't fit the new need.
I believe XMPP+Wave extensions allow to do all this, and do it well, so I don't see why it wouldn't.