I've read through most of this thread now.... wow, entertaining.

The pooh is really hitting the fan on this one.
My 2 cents is that this is a test only, which is why I think they have chosen one M&G each in 3 different parks, to see what type of uptake they will have to see if it's worthwhile pursuing an eventual rollout to all M&G's and potentially all rides.
I can see pros and cons to the forced scheduling of a M&G. On the Disney side, it gives them a ton more control over scheduling/breaks, etc... On the guest side, I think it opens up the possibility of a far more enhanced character experience.
The biggest negative I can see, from a guest perspective, is walking through a park with your child who happens to spot a character and spontaneously wants to meet them and can't, at that exact moment, because they have no FP. I think most M&G could probably have a lot of availability in a FP inventory (excluding the obvious A&E), so it's very conceivable that you could get a near immediate FP time and swap out a future pre-booked FP on your phone, or if you are past your first 3 FP, you need to get to a kiosk, which is a bit of hassle.
IMO, I think Disney should get a little further down the FP+ path and iron out kinks with the newly rolled out 4th FP+ and have that working on peoples mobile devices, then they can start layering in testing of FP+ Only experiences.
I personally, I think I would be fine with all attractions and rides needing FP, as long as I am able to manage it from my phone reliably. And I think
MDE is a long way from being robust and reliable enough for that.