They'll all use it, each and every human being, but of course only a few of us who actually do our own thinking will care enough to protect our own keys.

The most likely scenario, in my mind, is that governments will all be forced to back their local currencies with a blend of Bitcoin & Gold in their treasuries. So all paper currency will have a large percentage of Bitcoin backing, and that will be enough for most people. (Until govts take them off the bitcoin standard like they did in 1971 w/ gold.)

So since you can always depend on govts to lie and steal and cheat, in time it will be absolutely unavoidable for everyone to be forced back into full-ownership of their bitcoin, although that may take another 200 years.