On the sustainability question, bitcoin is a pure bubble, an asset without intrinsic value — its price will fall to zero if trust vanishes.
When trust vanish, and I think that it is pure impossible that the trust of ALL the user of bitcoin just burst and vanish without a reason. And if there will be a reason it might be because the government is continuing on trying to control the value of bitcoin by adding taxes on it and such things that keeps it regulated while the true nature of bitcoin is unregulated.
