I've thought about this for a while actually. I think the hardest thing to balance would be privacy. With a FOSS-oriented platform like this, and a broad amount of features like Facebook, you would have to have the users sacrifice a certain amount of real-world data to have these all be linked, and convenient. It could be encrypted in some way, so at least the instance's server wouldn't be able to read the data, but across users you would. I think a new line or definition would have to be made for people who want to use something like this. Most people, though, probably wouldn't care. And a FOSS version would 100% be better than Facebook's servers, where the data is mined and sold.