Someone else here made the excellent point that the high value flyers getting rewarded by Delta with all these miles are frequently those who have the least loyalty to any carrier and the least need for miles. These wealthy folks will choose based on amenities and schedule. They don't need the miles and won't be particularly motivated by them. Probably the only ones who will are those traveling for work in these classes, but as it was also pointed out, many companies do not spring for C/F travel. Thus, these people who travel in Y will lose out too.

The rest of us actually are motivated by the ability to earn miles. If this comes to UA, many of us, like me, will just fly less. Much, much less.