A very relevant scenario is Jetstar 787 pilots, most of whom will be in the top half of the seniority list, and many I would imagine towards the top of the list.
How does that work if the 787 is grounded or significantly clipped ? - I can't imagine a low cost operator looking forward to spending millions on re-training 787 pilots back on to the A320. Do they retrench redundant 787 pilots or from the bottom of the list?