I strongly and completely disagree. For a supposed next-generation, distributed open source application, language and version control choices are important. There are arguably valid reasons for using PHP, none of which you provided in either of your comments, but there is no excuse for using SVN. SVN has its place, and that place isn't in a project like this.

I'm completely down with the idea the SVN isn't a great choice, but I don't see what that has to do with the decentralized nature of the app whose source it's hosting. It seems like saying you should use XWindows to develop all network-related software because it uses sockets.

No. If your differentiating feature is a principle, then you can't ignore that principle.

Today, DVCS is essentially the foundation of developer social networks, both formally (github, bitbucket) and informally. How are you going to make a supposedly decentralized open source social network when the foundation isn't decentralized? Mom doesn't care right now whether a social network is decentralized and open source, developers do.