I agree with 1. Indeed I'm not sure bitcoin could be used simultenaously by billions of users.
Really?
You don't think if bitcoin gets really successful and there are hundreds of millions of dollars poured into engineering efforts for it (and if it is wildly successful, big companies WILL invest huge amounts of money on it), that any scaling problems won't get solved?
I bet I could find people predicting a few years ago that Facebook would never be able to scale to billions of users (it was written in PHP for pete's sake!).