Do we want bitcoin/cryptocurrency related questions?
Questions about the cryptographic mechanisms are fine, questions about economy, usage, acquisition, ... are not!
What we do with the questions of the latter kind depends on the exact instance. If the question is of poor quality to begin with and can't / won't be salvaged by edits, then closing / deleting it is the way to go. If it is of good quality, then migrating it to the appropriate cryptocurrency site is what we should do.
Actually, I think there isn't much more needed to be said (don't always need 10 paragraphs on Meta As).
As for the tag, we can have one and use it to group questions relating to the mechanisms, as all our other tags do (grouping things topically related).
Finally for the concrete question you asked about, it seems to ask about the cryptographic mechanisms and thus is fine here. Of course, anybody who opposes this position is free to write an opposing answer and / or VTC that particular question. Also I just went ahead and created and added a cryptocurrency tag to that question.