I hope they do abandon it, because I know I won't go anywhere near the source until they do.
The AGPL contains this little gem:
"if you modify the Program, your modified version must prominently offer all users interacting with it remotely through a computer network (if your version supports such interaction) an opportunity to receive the Corresponding Source of your version by providing access to the Corresponding Source from a network server at no charge, through some standard or customary means of facilitating copying of software"
Anyone that accesses your website is entitled to the source code you are using.
Indicating copyright ownership has nothing to do with the licensing. The people who wrote the software own the copyright. Being AGPL, or whatever else, defines how other people can use the software.
The question about Diaspora is about their requiring assignment of the copyright. That is, the project requires contributors to give away their ownership of what they wrote, so that the project owns it and can re-license at will.
Personally, I think it would be a shame. You're only on the hook if you want to modify their reference implementation, and aren't interested in sharing your changes with the community.
Write your own implementation under whatever license you want (and once they're a little farther along with actual protocol documentation, that ought to give you everything you need to make it happen), or share nicely. I'm not sure how that's a problem.
The AGPL contains this little gem:
"if you modify the Program, your modified version must prominently offer all users interacting with it remotely through a computer network (if your version supports such interaction) an opportunity to receive the Corresponding Source of your version by providing access to the Corresponding Source from a network server at no charge, through some standard or customary means of facilitating copying of software"
Anyone that accesses your website is entitled to the source code you are using.