I do see the the problem you'd face if they implemented a system like this. I know I originally posted this example, but I still don't believe they will do something like Max Pass. I believe it will be something like Universal EP, where the price is much higher and NOT included for on-site. You might get a better price by staying on-site though (depending on level of accommodations).
In your example, I assume you had 8 people for 10 days? While, yes that would add quite a bit to the overall cost, a trip of that many people for that length of time is probably not the norm.
IDK, but if I'm there for 5 days with my family of 4 and the added cost is $25pp / per day, to be in the best position to experience the rides, I'd bite the bullet and buy it. I wouldn't be happy about it, but I'd do it because the alternative would be to be at a disadvantage after spending all that other money to make the trip happen. A fee like that like would also make us re-think future trips though.
I firmly believe pricing it "low" enough to make everyone consider buying it will, in the end, just make it a WDW tax or a per person resort fee, not a benefit.
To quote a poster on another site:
"If everyone has FP, then nobody has FP."