Well, WN's business model has taken them from a small Texas puddle-jumper to a major national airline, so I would not doubt for a second that it could grow to the size of AA or UA with enough effort. That said, I dobut that WN would do such a thing, since their business model precludes service into most major airports. It's much more likely that UA or AA would shrink to the size of WN before WN grew to UA or AA proportions.