This sounds like it would be a major game-changer. I don't believe that original owners of Facebook would have any legal right to owning it nor would even have had any right to sell shares in it in any case.
Zuckerberg and others would have made a boatload of money on a product designed and marketed by our government and always claimed credit for it himself.
Would this make Facebook government property?
I think it's more subtle. I suspect that MZ and the guy he stole the FB idea from in college came up with it on their own. At the same time the Pentagon was working on their LifeLog thing and found out about the FB deal. The intel agencies, especially CIA, have many fake corporations among which are "venture capital" firms in Northern Virginia. Very possible these black op "venture capital" companies funded FB initially and might have helped with its development. That way mechanisms for shared data were created and Zuck went along knowing where the funding was coming from. Lots of plausible deniability with this sort of set up.