Almost certainly the A320. Its been said consistently, and it also makes a lot of sense for networking, fleet flow and crew positioning and hotel savings.

Therefore it won't be the A320, and instead, at the last possible minute, it'll be whatever soon to go away fleet that's getting new interiors (764, 717, ER?) only to be closed a year or two later to generate the MD's necessary for another beloved 365 to provide the flexibility to power out of the very manning crisis that opening then closing a base caused in the first place.

Canihaz MIP?