Business-wise, there's no reason FB wouldn't do something like a new SE. They have virtually everything needed to overrun Google in the long run if Google didn't continue to be ahead of the game, in a way we can't foresee.
Interaction - Google has a fraction of the necessary interaction which Facebook already has. Google is too information driven. They won't ever pull away the Facebook users for interactions such as picture albums, birthdays, wall posts, etc. Google doesn't have the platform for this, and would probably be cost prohibitive for them to try to create it.
This comes down to timing, imo. Google dominates information. Facebook dominates interaction.
BUT here's why it negatively impacts Google in the long run. Facebook can, far more easily, add information to it's database, than Google can create interaction. See, Facebook is founded on CREATING something, where Google simply relays it. It's simple for Facebook to add on things like SE's which are just relay systems. It's code. Code can be written. But Google can't simply CODE users to start interacting via it's database like they already do on Facebook; too much allegiance.
Facebook got lucky with timing because they created interaction, before information.
Pretty awesome study to watch though.