Burger King just doesn't fit the bill with what I think Universal perceives the CityWalk to be.
I think the ultimate would still be In n Out burger and I know it's never going to happen but if it did, I think it could be one of the most hyped food additions to either CityWalk or Disney Springs ever.
The one at the Linq Promenade i Vegas is forever busy, I've seen every table occupied with people eating on walls outside while restaurants next door are struggling to have more than 10 people in. Even Margaritaville just up the road only had 5 tables in.