So possibly like Fandalism?
If it's different enough from that, maybe doing it as an open source project will help attract the right people, and/or doing a Kickstarter to raise funds to hire someone full-time to work on it?
Building something like that is an entirely different prospect to taking on Zuckerberg.
> Also, the guy who ended up owning facebook (Mark Zuckerburg) is not
> necessarily the guy who thought it it up or built it in the first place.
Um... http://en.wikipedia.org/wiki/History_of_Facebook#thefacebook.com
Of course, if you do want Facebook to be history, it's not that hard - as I'm sure I've said plenty of times before, just provide me with a couple dozen clones and it'll soon be lying next to Geocities...