If I start having to pay full fare for TPAC and TATL Js, I will fly the airline that offers me the best combination of schedule, comfort, and price, and in most cases that will not be United. Of course that's exactly what I'm doing right now, but the value proposition is still titled towards United because of ease (for us) of GPU redemption.
This point really can't be overemphasized.
UA believes it can maintain existing business with substantially decreased incentives to frequent flyers below the GS level. It is surely emboldened by the reduction in competition following the AA/US merger. Whether its assessment of the market is correct remains to be seen.