For SEs it's easier since they get any seat in Y for free.
For the lower tiers, it's only free above a certain fare category, depending on status and route.
So the tough part will be the musical chairs that someone or some algorithm has to figure out to swap out GTEs and FOTSGs who would otherwise get preferred seats... and adding a feature for status pax in Y to choose their personal preference of "No, I don't want a Preferred Seat and would rather stay in seat 45E so please have your algorithm ignore me".