Originally Posted by FlyerBeek

Sure, but they would then be at a marketing disadvantage with AA/DL/etc having a domestic "First Class" product while UA's product would be labeled as "Premium Plus." People know what "first class" means - even if it would be the exact same product with a different name. For a while, I think DL was allowing connecting domestic segments to book into F on longhaul Premium Economy fares. That's probably a better option if United wanted to go that route.

-FlyerBeek