I think that if they did this with a return time, you should not be able to go on another ride while you are waiting. Think about it, if i'm waiting online, do I get told a return time to come back to it? Not unless I use my limited number of fast passes. If the person with disabilities, can not wait in a cool, relaxed designated area, I'm fine with allowing them to walk the park and come back at a designated time. However I do not think that their party should be able to go ride attractions with lesser wait times, until their time is met. That system is still unfair. Most people with disabilities just want to be treated fairly. They should not get these extra perks like being loaded onto buses without waiting inline or getting to the front of every line. You have to make the system equal and then no one will abuse it. If you can have a return time and still go on other attractions, people will still abuse the system. With RFID they can keep that from happening and anyone that is against that equality, simply wants to get to the front of a line.
I concur 100% on the ride passes, hopefully Disney works on this with MM+/FP+ for all GAC types to limit the fraud that does occur as the fraud hurts everyone and the guests that need the GAC the most. IMO the perception will not change though as regular guests will only see the wheelchairs move through the FP line and continue to get bent out of shape as though a GAC is a front of the line pass. There may be a small group that disagrees but I can attest my wife would MUCH rather get to partake in the new enhanced queues, and wait in lines than sit in a chair with little to no visibility except guests rear ends, not be shuffled to wheelchair areas where family members are LIMITED for parades/fireworks/Fantasmic/etc. and be able to walk around and enjoy vacation without guests staring at her, resenting her because they think she is getting something special.
The bus loading is a simple ease of access rule, if the disabled guest goes through the line, when it is their turn the bus driver would then have to stop, close and lock the front door, ask any guest sitting in the designated areas to move and then load the guest which can take as long or longer than allowing them to load first. Also, something everyone that brings this up forgets is that while you are running off to the parks or your room, we are on the bus another 5-10 minutes while we wait for ALL guests to unload and then the driver has time to let us off yet I NEVER hear anyone complain about getting to get off the bus first. I would NEVER consider getting to spend an extra 15 minutes, including the time it takes for us to unload, on a bus a PERK, is is insulting that you consider this is a benefit.
If there are more guests in line waiting than there is room before the disabled guest arrives, they should wait for the next bus and this has been requested by attendants at the stops at times when we have been there over Christmas breaks over the past few years.
More often though, we have been at resorts such as CB with multiple stops and repeatedly had guests refuse to move or drivers refuse to even ask or simply state there is not enough room to pick us up with my wife in her wheelchair even though she almost always offers to transfer. I personally feel that guests in parties with wheelchairs should NOT sit if their party is already taking three slots for one, ECVs are even worse as the guest is not even allowed to sit in them in transit. We have had waits of over 45 minutes unless we go to the first stop regularly and we are not the only guests that have had this happen.
To my point.... no matter what Disney does, there will be a perception that someone is getting something others are not, whether it is GAC, bus access, etc.