- I actually don't know what will be the numbering strategy after they run out of numbers on the current scheme. For the first series ("2002"), central banks fell quite short of being forced to decide on it: the last printed French tenners were U**99. Now, for the Europa series, they are running out of numbers faster. So, the central banks who might have to deal with this problem have probably already decided on that.
- YCNZ skipped "UI" on their hypothesis. Unless it's just a typo, I don't see any reason for the French printer to skip the letter I. It's already used in printer codes (shortcodes) and it's not easily confusable with the digit 1.
- I would guess that the next sequence won't start with G. Here's my reasoning: second letters H and X have been used (in Austria, Germany and Spain, until now) presumably to print test notes (even though some of them have been issued). I presume that these particular letters were chosen because they are the only ones which value is 0 (zero), in the checksum calculation. So, if they want to reserve H for test notes, than the second sequence of second letters must start after H. My guess is that the next sequence will be I, J, K, L, M, N. It's also convenient that it stops just short of the confusable O.
EDIT: I had written "last printed French tenners were U**95", after looking at giulcenc's 1U table. I thought this was not correct but didn't bother to check. I was sleepy… Trollix kindly rectified me.