I think several items already mentioned are my key reasons to be against this. It would be nice for Tahoe Girl to get free upgrades as my companion, but I think only those that never pay for upgrades would benefit overall. The people spending money on upgrades or flying enough to maintain EXP would suffer.

1. Standby upgrades would be next to impossible.
2. EXPs would suffer when other EXPs upgraded a companion ahead of them. Heck, I would upgrade a co-worker, friend, neighbor, anyone I knew on the flight, if I could for free.
3. With all the double EQM promos, lifetime gold and plat, etc, golds would have almost no shot at upgrades anymore. Plats would see their stats drop too.

If they allow people to pay to bump priority in their respective status waitlist, I would tolerate but not like it.

If they went to any system where you could pay to jump ahead of higher status people in the waitlist who did not pay, I would leave AA immediately. I would keep PLT for award flight benefits, and would use the free upgrades when AA was the best option, but I would not have any reason to stay loyal if I could be trumped by someone with more $. If they do that, why not just auction off upgrades to the highest bidder? That could make up a ton of revenue. Call it eBAAy.