The problem with this is that these platforms thrive because of their existing network effects. Even if you own your very own well built .com the vast majority of these dot coms will still have a combination of facebook, twitter, youtube accounts etc which mirror content available on your personal site. This provides distribution that is otherwise difficult to come across.

I have been working on a purposed solution over at http://www.peerprofile.com which allows creation of a personal domain and instead of getting locked in provides an open model.