With regards to the concerns over too many people booking double etc, that is why I don't think it will be available to more than a minority of guests. Most likely, as one pp mentioned in a linked blogpost, the 10 most exclusive resorts. If they gave FP+ to ALL guests, and even 1/3 to 1/4 of them used it, major chaos would erupt. Even the 10 most exclusive resorts would be say 15-30k people at peak times all booking FP's in advance. The consequences if one day half of 30,000 people decide to go to say DHS and book for TSMM (If that is included, I presume it will be.) could be disastrous. They already see increased wait times on some days in certain parks as a majority of guests visiting the parks choose to go there (for whatever reason) this system could make things a LOT worse for FP+ users and non-users alike. Guess we have to wait and see how the testing goes. I just hope they don't take a small test to be reflective of how the major roll out would go.
For example, if a majority of guests had access, how would they deal with Food and wine? The majority would most likely go to epcot. Or if MK only has certain shows/parades on a few times that week, those parks could be overloaded with FP requests for the main rides. I'm curious as to how they would manage this beyond just 'limiting' one person to say one FP an hour. This could help, but I don't think it would solve it completely. Even then, I imagine some angry guests being told there are no FP+ reservations left for the big rides. Ironically, if you can book them far in advance, they could run out of them faster than normal FP's which can only be gotten on the day, if they decided to go with a tandem system. Would the people who couldnt get FP+ for the main rides shift to using normal FP's and further bog that system down? Just a rambling thought.
If they do open it up to more people, I sincerely hope they put a strict limit on the number of FP+ bookings, preferably more than the 1 an hour currently being mooted.
Looking away from technical details for a minute, I still just can't see myself ever using this system. I'd like access to it in case it made me HAVE to use it, but until then, I and many of my friends I suspect won't bother since that kind of planning is a little too far. Makes me even more suspicious they will charge to recoup investment, if they don't see a big uptake in bookings.
Then again, I heard that Disney are cutting discounts on stays there from this year on, so maybe that is the 'charge' for this system?