All PL commands will be available, subject to seniority, to any pilot on the seniority list, irrespective of how they got there
I am being literal when I say I am confused by the proposal. Someone way back in the thread (maybe you, HF) said that to join mainline and bid across would possibly be a quicker route to a PL command than to join PL as an FO. Someone else mentioned that BA seniority would be frozen whilst at PL - so that PL commands would be out of bounds to PL pilots for as long as there was a single mainline pilot wanting to bid. Or it would be a quota which would go to mainline FOs, like GSS' 2/3. All the above would be unacceptable to nearly all potential FO recruits (save for the most desperate)
But if seniority rises from day one of joining PL, then that would silence most critics. It still doesn't answer why anyone would want to join PL as an FO when they could join mainline on much better terms. Maybe because of lower entry standards for PL? - dangerous ground!...