Actually I'd rather prefer someone to not invent the next Facebook. It reveals the human trait that despite best intentions, when shareholders get involved, cash is king regardless of the ethical stance the company supposedly takes.
In my mind, ideally the next big social media platform will be P2P and open source. I have some ideas on how this might work and the features this would include, but I've never hashed them out since my programming ability doesn't approach the level required for such an undertaking. Maybe I will as a thought experiment and publish my ideas so that anyone can use them.
And there are numerous nodes you can create an account on -- no need to be self-hosting. Though with FreedomBox, that would actually be pretty tenable.