There's also the issue of services onboard. When the people in row 428 (who have to pay for a drink of water) see that the people in row 427 get complimentary soft drinks, this is not going to be good for public relations. The fact that row 428 paid half of what row 427 paid is of no consequence to these people. What they know and see is that the row in front of them got something "free" that they are having to pay for. And, don't think that people won't be po'd. I still encounter coach passengers on occasion that are upset that the people in the front cabin got a "free" meal. We haven't had meals on a tray in coach since shortly after 9/11! Within the rank steerage seats, just wait until a f/a in a forgetful moment of compassion gives a row 428 or higher passenger a cup of water so they can take a pill. All hell may break loose among the other steerage seats.
Airline within an airline--particularly on the same a/c in the same cabin--has never been successful. We (AA) have that Main Cabin Extra for which people pay extra. However, as soon as the door closes if there are empty MCE seats (and there almost always are), people from the "common" main cabin seats move to them. So what have we gained?