The point raised here may be of more importance more often than TC implies. Everyone will be doing the ATPL ground exams (no one offers CPL ground school), but there are a number of other hurdles that need to be jumped before someone is given a JAA ATPL(H). This includes an IR and significant multi-crew (not multi engine) time. Lots of perfectly suitable pilots for ASU work will not have the money or relevant experience to get the full JAA ATPL(H). Time will tell, but my guess is that PAOCs will start to revise the experience parts of their Part 2s as time goes on
Incidentally, TC is right that those of us who do hold CAA licences will be able to get like for like CAA new licences. What I should have said was that if we did try to apply for JAA ATPL(H) licences many of us would not have the necessary combination of IR(H) qualification and multi-crew time.