Non-mathematicians have difficulty picturing sums like 0.00014321 BTC, which would be 143.21 XBT if XBT=100 satoshi(s)
The transition would be even more seamless because people already started thinking in bits. If 1XBT=1bit=100 satoshi, it would all make sense.
I like this too, and think it is the best option.
However, an alternative is to try and get two ISO codes, with XBT for 1 bitcoin and XBU for millionths (which would be used in existing financial systems).