True enough -- there is unfairness any way you do it - Length of stay gives advantage to those with more disposable income, a time based system gives advantage to those who are more available at that time.
Think about how crazy the "grab your reservation at 7:00" thing is --- equivalent to the mad Black Friday rushes. The doors open at 7:00 AM and there is a mad rush to grab the FP you want except, unlike most of these sales .. there is no LINE .. everyone just sprints at the door at the same time!
The main issue is the 'need' to do a Fast Pass at the exact first second or get stuck with poor times (or no fast passes for some attractions) - same as anything nowadays with high demand - buying concert tickets, getting your zone on Southwest Airlines, getting that Black Friday sale item, securing that ADR, etc. Year over year, as people learn how the system works, they will try and get there earlier and earlier ..
Not sure how they can handle it .. demand is just too high. They've created a highly sought after commodity in Fast Passes (which is why they are trying to monetize it with EMM and such) Someone will always try to be first in line and when demand that high, the rush to be "first" in line will be high.
The only equitable thing I can think of (and probably less strain on the computer system) is an old-fashioned lottery system - (similar to how I remember getting concert tickets at the record store back in the day (dating myself a bit, I know).
A convention I used to go to has gone to that system for reserving hotel rooms. Demand was so high to be "first" in line to get the "best" hotels close to convention center that the system just crashed and overloaded, causing a mess and frustrated customers.
So now they just give you a random number that determines WHEN you can go online to do your reservations. Thus spreading out the users in a more orderly fashion (a queue) and not based on "who is first" or whose internet connection is fastest, but simply randomness.
For example, I could see it working this way for Fast Passes.
A week before your 60 day window opens every
MDE account that check-in date gets assigned a random number. You are then given a time to do your FP selection based on your random number. (The first 100 people can make their selections from 7-8, then next 100 from 8-9, etc. etc.). You know where you are in line and can plan accordingly to be available at that time and have a good idea what your chances are of getting certain fast passes.
Yes, there would be just as many people that would find that equally unfair - especially when they find themselves at the back of the line or getting a time that is inconvenient to them.