people just need to have trust that government would accept the tax payment in that currency and at that rate to the other, paper, currency if it is still around - very low bar of trust for a government to meet and it would provide strong bottom line value for a currency. Especially if some deflatory (or limited inflatory) machinery is algorithmically built-in (bitcoin-style) so the government couldn't "print" the money faster than some limit.
Interesting variant would be a 2-tier system where government would accept only bitcoins "printed" by the government while allowing other bitcoins to be circulated as well.
My main point here is that whatever technology achieves is ultimately made to serve government as well (or sometimes almost exclusively).