I will probably open a can of worms here, but here it is :
Disney has always given Fastpasses for free when Universal sells their express and unlimited passes.
It would be an unpopular move if Disney started to sell FP+ (or part of it, like an additional FP+ slot for a fee)
But what do we see here ?
We see guests, who are eager to test the system, and who "bend" the testing rules by booking one night at a participating resort, just to get the MagicBand and be part of the FP+.
I'm not judging or arguing about those who pay for an extra night at a resort they won't check in into, it's not my point. My point is to say that guests have sent a message to disney, and this message is that some of them are willing to pay for FP+, and they do pay for FP+ right here, right now.
This message is flawed, because of the ability for double dipping, and of course for the hype of getting a MB (it's so frustrating to go to WDW and not being able to get something other guests get)
But, nevertheless, the message stands, and it says that charging a fee for FP+ would be absolutely possible, and if done in the right way, it could even be popular .... go figure .... because right now, some guests are actually paying $100+ to be able to use FP+ ... for a family of 3 the cost of one night at POP to get access to the test is about the same price as a universal express for the family
so I guess anything is possible, but guests have definitely shown disney that "paying" (indirectly) as much as universal was ok for some guests
(once again, just stating facts, not judging or pointing a finger)