The problem for us trying to figure this all out or predict results is we don't have much info on what is actually going on. We are like ancient people trying to predict the weather with only our ability to look at the sky to interpret the patterns. Disney on the other hand, has over a decade of data on fast pass usage to start off with. It's a safe bet that going into this, they are more prepared than most of us think.
Putting that aside and considering the data they'll collect, it's also a safe bet the new system will become extremely efficient over time. When they know how long it typically takes to get from the front of the park to an attraction, they can predict when a person who made reservations for the day but say, left the park for lunch (which the bands can tell them) won't be back in time for a FP+ and clear that usage for someone else. Heck, if you are on property and the bands detect you in another park in line for an attraction with an hour wait two hours before your FP+ window is up, they may be able to re-use your slot at that point. I'd imagine the system would be conservative enough to allow for the rare handful of people that defy the averages and run at full speed to get to stuff. To that end, I'd think the current FP system over-books tickets based on numbers Disney knows about what percentage of people who get FP tickets end up not redeeming them, already and we just don't know about it.
As they find new data points to examine, they'll be able to tweak this system far more than they ever could the old one. After the first six months of usage, their model for traffic patterns will be fairly reliable. A year in, it'll be even better. Five years in? (if not sooner) They'll be using this system to predict staffing needs for the Emporium on Main Street in late afternoon on the first Tuesday of the month because this system will allow them to track even the people without armbands by being able to predict what parts of the park a good number of guests will be in at given times and who has time to kill based on where they are with their current reservation, where they have to go for their next one and how much time they have between the two.they will eventually saves nod make money off this system in ways we can't even begin to comprehend... Being able to steer large percentages of people away from certain attractions, shops, restaurants, and restrooms during certain times of day in slow periods so they can cut down on staffing, for instance by placing people with reservations in other parts of the park. Nothing is 100% but if they can get even low percentages to follow the predicted patterns, it could have a major impact.
Of course, some won't stick to schedule and will loose their reservations and throw some of that planning off. It already happens today so of course Disney knows it will happen in the future. But the more live experience they get with the system, the smarter it will get at predicting and preparing for that, too - it's just logistics... All I'm worried about is the day FP+ becomes self aware and the animatronics revolt. Who would have guessed Skynet would start in a theme park?
As for off property guests being able to book in advance, the problem I see there is how does Disney know who you are? How do they even know you really plan to be there the day you try to get your FP+ for? With people staying on property, you've booked your stay so they know you will be there the day you make your reservations for. You are in their system and the bands you get are already linked to the account you booked your FP+ through when you get them.
The same will be the case in the future for APs - you'll already be in their system linked to your card/band and even though they don't know for sure you'll be there when you say you will, they at least know you can be since you have a ticket in-hand good for that day... But off property, do you even have tickets 90 days in advance? If so, how do they link your account to those tickets? I guess there could be a process where you create online accounts and look at tickets to enter serial numbers but I don't see most people bothering. If not linked to tickets in advance, how do they know John Doe that registers on their site and booked FP+ even plans to come the day they are doing this for? If they come, how do they quickly link up the tickets he bought that day to the FP+ reservations he made months ago? People complain about the reservation system for restaurants being bad. Imagine how hard it would be to predict anything if people could abuse this like that and steal times for attractions at parks they don't have tickets for and probably won't even be visiting on the dates they make reservations for.
My guess would be that even if they ever did roll this out to "everyone else", it would require them to have tickets in-hand at the time of setting up the FP+ which I would imagine most people not staying on property and not having annual or seasonal passes don't do (but I could be totally wrong). Otherwise, why does every hotel in the Orlando area have places selling park tickets?
Really if you aren't staying on property, why would you buy tickets in advance of your travel? I'm sure some people do but I don't know what the benefit currently would be besides avoiding the lines that may or may not exist at the park entrances and if you're that concerned with planning for convenience, it seems you might already be someone who wants to stay on property, anyway, right?
