I've tried to think of what is the quickest way to transition offsite guests and i think for the interm it would be to still allow them to show up to the gate with their paper tickets or plastic cards and when they enter the gate a CM will hand them a grey magic band coded for offsite guest. they would be able to then go to town hall or different checkpoints and put a cc on the magic band with a pin but to start it would be basic, allow for fastpasses and anything they preset up on the my Disney experience site. eventually I see magic bands being shipped to resorts offsite that will be inactive until linked with a confirmation # from a purchased ticket through Disney's site.
I should chime in on the best bang for your Fastpass+
MK: Splash or BTMR, Peter Pan, Space Mt.
Epcot: Soarin, Test Track & Do Soarin or Test Track again, everything else is walk on if you time it right.
DHS: TSMM, ToT, & RnRC
Ak: EE, Safari, Kali River Rapids (if warm out), Dinosaur (if not warm out).