The issue/problem isn't one of the technology (or of the ability to get advanced FastPasses/room keys/ADRs/etc.). The issue is one of implementation. If they implement a system that allows a user to set up an entire menu of FastPasses for their whole trip six months in advance? That would be (IMHO) a HUGE failure. But that's why I don't think they're going to go with that kind of implementation. If I had to guess, it would be something more like:
-Advance check-in, so that you get your room keys mailed to you in advance, if you want. You give them a cell phone number and they'll text you when your room is read, just like they do now. But you'll give them the cell number when you make your reservation. So there's no need to go to the hotel front desk first, unless you want to desk check your luggage (and you didn't use Magical Express).
-The ability to select one FastPass experience/day in advance. Get a FastPass for a ride OR a show OR a character meet & greet. The net effect is to allow advance-planning/once-in-a-long-while travelers to relax a bit about being able to experience something that's really important to them to experience with a minimum of hassle, while at the same time preserving some level of spontanaeity for other guests.
I don't have any inside info, and I could be totally wrong. But I just don't see the big picture benefit for Disney to introduce the administrative headache that allowing every on-property guest to plan their entire vacation including FastPasses six months in advance would bring. It's enough of a mess juggling 180-day advance ADRs. On the other hand, if you knew that by staying on property you could get a FastPass to a talking Mickey meet-and-greet for your preschool-aged child, (or Space Mountain FastPass for your teenager) wouldn't that make you more likely to pay the on-property premium (with a consequent net profit increase for Disney)?