Mr A,
5 earlies is already possible in CAP 371 - its just you don't choose to use it because of the extra strings attached like not more than 9 hours duty and the extra time off needed - Brown Book 7.7.2.1 if you are interested. Sub part Q is unlikely to come our way as sensible countries have decided they don't want to be dragged down to the lowest common denominator and they realise that when people are tired at night in charge of machines people start dying (ask Gary Hart).
Yes easy do it - that's why their management have just agreed to go to 5 on 4 off 5 on 4 off because all their pilots are so knackered despite all their days off - nothing to do with the fact that their days off are midnight to 6 am rather than our 9 pm to 9 am of course.