The transition does indeed matter a lot. I think there are other transition methods you are missing though. Look at how the US switched quite quickly to chip readers. I could also imagine a system where US dollars (or insert currency here) and UBICoin exist together for some time, but dollars are only valid if you were born after year X. Merchants would accept both during this transition time with an exchange rate.

There is a ton to discuss in terms of transition. I don't think the transition being another unsolved problem invalidates the entire idea, particularly when virtually no time has been spent examining the transition options.