That plugin's a good start. It's only been downloaded 708 times, though, possibly because it's not being actively developed or promoted, and perhaps also because it has a long list of dependencies that would make setup too hard for most.
I think it could also be a branding issue. If I was building a distributed OStatus-based social network on the back of private WordPress installations, I would:
1. Market it under a different name than "OStatus". WordPress users need not know that their blog is automatically syndicated via RSS, and users of this new social service need not know that it's powered by OStatus. It is easier to market ideas than it is to market technologies and protocols.
2. Present users with an interface they're familiar with from other social networks, without stealing intellectual property.
3. Create a pretty marketing page that sold the project on its merits as a free social network that nobody owns. Give it a mascot or a bold logo.
4. Encourage the thousands of WordPress-related blogs to write about it, with a goal to drive WordPress developer adoption that might trickle down to other WordPress users too.