You act as though this is the first time in Disneyland's 57 years that things can get stagnant. How do we know this is going to happen? And if it does it certainly will not be the first time this were to happen.
As I have stated numerous times DL has a large enough local base to where it doesn't need to have national recognition as much as WDW does. And WDW physically is a lot more difficult to go to - you have to travel to there to enjoy it.
If you are expecting us to be up in arms that the DLR is going to slip to #2 it's not going to happen. Disneylanders just don't look at the park as some type of national vacation destination. They see it largely as a locals park to take a day trip or at least a regional park to make a weekend vacation out of or as part of a more generalized Southern California vacation.
DL has weathered the stagnation storm before. But it shouldn't worry if USO takes it spot. It needs to sorry more about USH doing that. As USH grows and DL remains stagnant - that should be what we are worried about. Because if this causes the DLR to become #2 in Southern California then Disney will be in a world of hurt.