Back to the real issue! :P
Assuming they're offering a full menu and using the current machines (which I REALLY hope they don't resort to the cheap Bagel Nosh-style machines they use around the resort for the "mochas"), it could create a backup, unless they were extremely efficient at calling out orders, calling the line, and prepping the drinks with a bank of machines. Prepping and making in bulk Caramel Frappucinos and Iced Vanilla Lattes wouldn't be preferable, but it'd make sense maybe in this situation.
And agreed ... no matter the location (Fantasyland Skyway chalet would be amazing), Starbucks has been ingrained in our heads as a "third place" ... where it's okay to linger for hours. Of course regular guests wouldn't do this, but AP's deffintly might, especially over a hot chai on a cold day (I know I would). Again, it'll be interesting!