I rarely see much abuse on domestic flights - most people have one bag but there are more than a few like myself that have a 22" suitcase and a backpack/large handbag combo. Maybe 1 in 100 has a third item and maybe 1 in 50 a suitcase that will not fit wheel out in a standard 737, 757 or 319 bin. So I think the abuse part is overrated. For international I normally fly paid C and sometimes have a small shopping bag with duty free when I'm headed home in addition to my 22" and swiss laptop backpack, but I have never ever seen the Polaris bins 100% full - usually the opposite with plenty of open space. So I'm not taking anyone's space with my duty free or even my backpack when flying TATL or TPAC.

As for the "policy" I've said it before and will say it again: I fully expect to put both my items in the overhead bin, and think I've earned that privilege, both through status and by flying on full Y domestic for business and paid C international. If UA decides to mandate that all 2nd carry-on items must go under the seat, I will switch to another airline for my domestic travel. That's non-negotiable for me. I don't check bags except on Qantas where I have no choice (or on a ski trip). I could not care in the least if a Group 3-5 customer has to check a bag because the bins are full. Better them than me as they probably paid less and have no status.