OP, I share your concerns/anxiety. We are planners, and the "old" system worked really well for us...
With FP+ the main benefit for us was that we could book FP+ for the afternoon and not have to worry about getting to the parks early which is a big benefit when you are coming from the west coast.
I really don't care what kind of system they put in place. What I care about is how long I have to wait in a line (20+ minutes is a no go for me) and how much I can do in a day.
...largely because of Doug's first statement above. To me, it is very relaxing to have everything planned out before we go. Having a dining reservation and 3 FPs all after, say, 5PM, allows us to have a late night, sleep in, enjoy the resort/pool during the day, and enjoy the parks at a leisurely pace that evening.
We bought
DVC so we can stay longer and leverage our APs to follow this kind of a schedule on most days instead of constantly rope-dropping and over-scheduling. So I think the OP's concerns are valid; I've had similar thoughts of "what-if they change x, y, or z" (which has led to considerable anxiety).
As for the MaxPass system at DLR ... I enjoy the system a lot out there, but I don't think it translates well at WDW. The resorts are too different; the two big ways I can think of are size and clientele.
Size: All DLR on-site (and really off-site) hotels are walking distance, and the parks are side-by-side. It is comapct and much easier to get around, pop in early and go back to the hotel, etc. As long as you get into one of the parks by early afternoon, you can snag a FP for any attraction (on most days). I can't see it working like that at WDW ... I think you'd have to be at parks within an hour of opening to get Slinky or FOP, for example. And that means committing a lot more time due to how spread out WDW is.
Clientele: I'm referring to locals vs. tourists. I think MaxPass works really well given that there are fewer tourists at DLR than WDW. It's a more casual experience at DLR. But with so many more tourists at WDW, I don't see a MaxPass (i.e. "day-of") type system working as well.
So looking ahead to what WDW rolls out, I hope that:
- ADR's come back and move to 60 days permanently ... 180 was ridiculous.
- They institute some sort of replacement/modification that allows you to pre-schedule certain attractions ... whether it is FP+ or something else.
- With both of the above, I think you should be rewarded for length of stay ... i.e. ADR's at 60 days + length of stay ... same goes for FPs, or whatever the replacement is.
For me it really comes down to what Doug said above ... "What I care about is how long I have to wait in a line and how much I can do in a day." As long as that isn't negatively impacted in the long run by whatever the updated system looks like, then I'm still in. And while I do have some anxiety about that right now, I also trust that WDW won't make things worse (i.e. I am hopeful/optimistic to see what they roll out).