C'mon, while they have a very good idea in theory, I don't think it could work. The general public is not quite ready. It's too technical to host your own node and there won't be a critical mass who can figure out how.
With enough work, it would be as easy to set up (or easier) than any other blog. The connections to other diaspora instances would be as easy as logging into OpenID... Just visit their page, put in your URL, request a link, and wait for the other person to grant it. It could also be done the other way with putting their link into your blog, and having the backend take care of it. I'm sure there are other ways, too.
So yeah, it could work. Not in that short amount of time, but it could work.
And they wouldn't need the critical mass: the plug computer could come with a blog engine, bittorrent (client and tracker), a mail server for the family… It could be the Eben Moglen's freedom box that inspired them to start Diaspora in the first place.