Comment by WorldMaker

As I recall, at one point Wave sort of had enough of an XMPP bridge that you could terribly IM a Wave without having a Wave invite if you were one of the 20 people still using XMPP that month and your friends with Wave knew a "secret" @ mention and you felt like learning an XML mini-DSL of pseudo-commands and kinda-unidiffs to read the changes from the people actually in Wave.

There was also plenty of talk about the "eventual" email bridge and real multi-server Wave federation, neither of which properly happened. (At least not in the invite months).

Though, yeah, Wave really could have used the network effects of non-scarce invites, because it wasn't as interoperable or as much of an "open standard" as it wanted to be. Or it should have had all that interoperability and open standards properly ready at launch and the Google server could have just been sold as the "best" of several options (and people waiting for invites could self-host; that might have done enough for viral class projects in college environments).