Optimists believe that the rate of Bitcoin in a couple of years (possibly tens of years) can generally reach up to 100 thousand dollars for 1 BTC,
being an optimist would have meant saying something like price will reach 100 thousand dollars for 1 BTC in one year not 10. actually i say 10 years is the pessimistic view.
I think that this is quite realistic if the governments of the countries can agree among themselves and make it legal.
the a couple of more countries adopt bitcoin (because bitcoin is already legal in almost all countries) the price would get there faster but it is not a requirement at all.
A favorite counter-argument among optimists is a comparison of Bitcoins with real gold (they are often called "virtual gold"). Remember the demand for real gold. Once $ 300 for one ounce was considered very expensive. During the 2008 crisis, gold rose and reached $ 1,800 per ounce. And what is gold? Than it is provided? It's just metal. Bitcoins are also not provided with anything. However, the potential opportunity to make it an international currency makes for it unlimited growth prospects.
it is usability of both gold and bitcoin that makes them useful and price comes from that usability. otherwise if gold was just a metal without any usage then it wouldn't have been worth this much.
