If WDW charges for FP, I might pay, or a might decide the price isn't worth paying. It depends what it costs, and how much it improves park touring.
Bingo. And this is true for everyone. But it appears there is a fear that people will be priced out -- which is likely true. There are people who will eat Ohana, signature dinners, buffets, every day. There are those for whom it is a costly splurge to do it 1 night, and there are people who won't or can't afford those restaurants.
There are those who are willing to pay $2k for a VIP "tour" which is really nothing more than a day of line skipping.
The higher they price it, the more people will be excluded (either because they can't afford it or because they don't find it worth the cost).
But it's like the current debate about EMH vs Extended Hours. For guests who do pay the premium to stay at deluxe resorts, they are mostly happy -- By being more exclusive, it should be a superior experience compared to EMH which included more than double the number of qualifying guests. But for those who only budget Mod/Value or "neighbor" hotel, they feel that something is being unfairly taken away from them.
It all reminds me of a line from The Incredibles -- "If everyone is special, it's just another way of saying nobody is." -- You can't give an "exclusive special benefit" to everyone. The more exclusive it is, the better the benefit can be. Giving "everyone" essentially the same Front-Of-Line privilege really has made for a pretty weak benefit.
On the other extreme-- the only people currently getting Front-Of-Line privileges are basically Club 33 and VIP Tour groups. So paying $30k per year or $2k per day does give a very special benefit.
So if Disney does indeed "monetize" Fastpass.... it will be a question of where on the spectrum it lands. A weaker benefit at a lower price, or a bigger benefit that is more exclusive at a higher price.
No matter where it lands, there will essentially be 4 groups of guests:
1 -- Guests who love it, because they are happy to pay for a superior benefit.
2 -- Guests who can afford it but buy it begrudgingly, and feel they are being forced to buy an overpriced benefit
3 -- Guests who can afford it but decide against buying it. While upset about missing the benefit, they found it overpriced.
4 -- Guests who really can't afford it, who will be upset that "Disney is pricing out regular people like them!"
Pretty much no matter how they design it, people will fall into those 4 basic camps.