Originally Posted by emcampbe

This isn't quite correct. Revenue-based mileage will be applicable to all UA-operated flights no matter who tickets it, with the small exception of bulk/tour tickets that earn mileage, which will be a percentage based on the fare class (as low as 50% for the lower fare classes). Ticketing UA flights on AC and crediting to MP will make no difference to the mileage earned. However, for non UA-ticketed non UA-operated flights accruing to MP, they will continue to be distance-based, assuming its in a class eligible for mileage accrual in the first place.

It's not hard for UA to track spending when they are operating the flights - revenue is still broken down by segment, and this kind of calculation is already being done by UA. It calculates this for PQD for US-residents today, who are accruing to MP on UA-operated flights ticketed by other carriers.