Originally Posted by
JonNYC
They'd have to grandfather (or free upfare, etc.) tickets already bought, but then eliminate or reduce EQM earning on some of the cheapest fares going forward (in addition to the other takeaways from those cheapest tickets.) No much bigger changes really needed at that point.
Delta just introduced a new fare class (E) for basic economy. I'd think that would be easier than (for example) AA making S fares highly restricted in this way. No tickets would have been sold in this new fare class without the new rules, so no need to grandfather anything.