Okay well, what all the others said about banning.
With regards to fast pass plus, I haven't yet decided what their end game is yet. First of all, I think in a way they were simply desperate to figure out a way to throttle attraction access, because their attendance keeps going up and they aren't adding rides. (I have come to realize that the much larger crowds the last couple of years at WDW were really due to the HP-WW expansion at Universal luring them to Orlando. Disney hasn't done anything differently since 2011, that they weren't doing in the years before that, to suddenly and so drastically overcrowd their parks. After HP opened is when we began noticing the huge change in crowds.)
Resort Guests: One thing I know they CAN'T do is anything like what Universal does, which is permit Deluxe level resort guests front-of-line unlimited ride access. This only works at Universal because they have an extremely limited number of Deluxe rooms: 2400. Assume 4 guests per room at full occupancy and you only have 9600 people per day with unlimited resort guest front-of-line privileges. (Note that the new Moderate, Cabana Bay, will not offer the front-of-line Express Pass privilege.)
By contrast, Disney has 8328 rooms in their "Deluxe" category alone - not including DVC units (~3000), which probably should be considered Deluxe due to their nightly rate if rented. But we'll ignore DVC for now. Assuming 4 guests per room at full Deluxe occupancy, that means that 33,312 people would have front of line privileges. I can tell you right now that if 33 thousand people could go to the front of the line over and over on Soarin, Test Track TSMM, and the Mountains, nobody else would be able to ride without a 3+ hour wait. Not the people in the other 22,077 WDW rooms, and not the people staying offsite. There is NO way Disney can ever implement the deluxe resort guest policy that Universal has without causing riots in the parks.
So that brings us to the second form of Express Pass Plus offered at Universal, which gets offsite guests buy their way to the front of the line. The cost of this pass varies by season but the most it ever costs on the highest of peak days is $119, I believe. The average is somewhere in the 50's - 60's.
My opinion is that anyone who is wealthy enough to pay the rates at a Deluxe WDW hotel, or buy/rent DVC, is wealthy enough to pay this much for front-of-the-line access as well. And without question they would do so. In addition, many people would "step down" to a moderate or a value and use the savings to fund the express pass purchase. So you would end up with tens of thousands of people in each park with front-of-line privilege. This obviously would not work - again, riots in the streets of the parks as people who "paid not to wait in line" would be waiting in line anyway.
Could Disney limit the number of passes they sell per day? Universal does. Would this work at WDW? No, because the demand for them would so greatly exceed the capacity that the darn things would be a ticket scalper's dream. If they sold them in person there would be fighting in the lines. If they sold them online they'd crash webservers. If they sold them by lottery, you'd have to enter a new pool for each day of your trip. LOL.
So we know they can't reproduce Universal's model. We also know they can't go back to a model where they give you a ticket book and limit you to one ride on each attraction per day - once unlimited standby riding is in place, it's not something you can take back, unless you're willing to drastically cut your park admission prices at the same time (and they wouldn't do that either).
So what's left? They can't limit riding overall, and they can't give free unlimited front-of-line access to their higher paying resort guests. They have too many people in the parks during moderate/peak times so waits for desirable rides can easily climb past 1 hour during moderate times, into the 2+ hour range during peak times. If you don't believe that their only motivation for FP+ was "people would spend more time and money in the shops instead of lines" - which IS what they told analysts in calls - then all that's left is that they are secretly preparing to sell fast passes in some way. And there's no evidence of that in their official earnings calls and discussions.
Even if they did it, how COULD they do it? They already have tiering in place, limiting guest selections for popular rides. They give everyone 3 passes, with the only benefit resort guests get (no matter the resort type) being that they can pick 3 rides ahead of time, instead of wasting time at a kiosk on the day.
So working within the confines of this current FP+ system, all they could do would be to perhaps give Deluxe guests more fast passes per day than Moderates, and Moderates more than Value, and Value more than offsite. 6-5-4-3. And thanks to human nature, they could actually pull this off. Pretty much a guarantee that any value guest who posted on here that it wasn't fair they only got 4 passes would get jumped by people saying "if you want more, pay moderate or deluxe like we do". Could they give moderate and deluxe resort levels additional fast passes, and ALSO allow them to pick multiple rides from the top tier? Sure. If you stay in a Deluxe hotel, you can pick 2 rides from the top tier, so you can get fast passes for both Soarin and Test Track. And again, they could pull this off because anyone who complained about it would be told "upgrade you room, then".
Could they do as the OP says, and introduce ANY kind of payment system that isn't like Univeral's (which we know won't work)? Could they continue to give each guests 3 fast passes, and charge a la carte for additional ones? There's no way that could work. The problem is not that people would be unwilling to pay, it's that Disney doesn't have the ride capacity to support it.