Social network federation, or compatibility, is a good goal for users, but the main barrier to its implementation is that the big players - Facebook, for example - have an active interest in not supporting open standards. Keeping people locked into Facebook because all their friends are there has been the main competitive strategy of social networking sites from the beginning. The business plan is basically set up a website, attract a self-sustaining critical mass, then lock it down so the competition has no hope.
Federation means that it doesn't matter what network someone is on. It makes step 2 (critical mass) moot and openly mocks step 3 (lockdown). That's just not going to fly with the big players unless, for instance, the open network of competition grows far beyond them. That's the point that the critical mass shifts from Facebook to the open network, then everyone starts maintaining two profiles, and eventually abandons Facebook because not everyone is on it any more. So if you, as a small social network, want to topple Facebook, your best bet is to throw in your lot with the rest of the federated network and be part of the new majority.
Mokalus of Borg
PS - Then Microsoft, in their Microsofty way, will "embrace and extend" the standard.
PPS - Their proprietary extensions are compatible in one direction only.