I cannot see the whole world using bitcoin when its going to create such wealth disparity.
There are roughly 13 million coins in circulation, with the maximum amount being 21 million. This means over 50% of all coins in being, are in control of a small minority consisting of maybe 0.01% of the worlds population.
Nobody will care- If bitcoin is useful enough and easy enough.
Will they though? Yes, it may be useful and easy, especially with the introduction of smart contracts//derivative coins etc...and will therefore cut inefficiency of how the human race in general manages itself, but people will inevitably care if the value of everything they have worked for, suddenly runs into the hands of the few elite.
You can argue that there is a rich elite at the moment which is absolutely fucking the world right now, but the amount of potential disparity that bitcoin may create will be absolutely catastrophic, causing the human planet to turn all dystopian. I know this sounds like something out of a book, but this could happen, especially if no single authority has control over this object.
People will care if their $10 turns into the equivalent of $0.01 cents in bitcoin, which is the case if bitcoin is to flourish. But this is just my opinion, and maybe it will change with a bit more understanding...