I think your best chance is to build a community (or 'network') that is focused on a certain niche or group of people though.

And I guess the whole 'scaling' aspect can be quite 'scary' when you look at sites with millions of members such as Facebook but I'd say screw that for now and just get started, by the time you really need to expand your infrastructure, things (such as your team, capital and so on) will be different anyhow. In order to avoid any downvotes: of course, keep scaling in mind. But put the main focus on your ideas and the overall experience.

And regarding the demise of Facebook in general: hopefully. I really dislike the corporateness and general lack of 'coolness' on Facebook. Myspace felt a lot better and was tons more fun to me than Facebook, all technical and visual shortcomings aside.

I can't imagine anyone 'feeling at home' on Facebook.