Wheelchairs can appear much wider than they actually are. I recently toured a public building with a wheelchair-bound friend and was shocked to see, over and over, how she sailed through spaces that I thought looked much too narrow for her chair to fit through.
It depends on the wheelchair. I have a newer powerchair (with a tilting base) that is 26 inches wide and a lot longer. (I do not bring it to Disney but instead use my petite 22" chair.) The new one, while comfier, is really too big to maneuver well into my HA van or tight corridors. An ADA pathway is supposed to be at least 30-36 inches wide. The "tightness" comes when you round those corners of Buzz or Finding Nemo. The wider the wheelchair the wider the turning radius required.
Since Disney is lumping ECVs into the wheelchair category, I honestly think they need to redefine what they consider an ADA queue. An ECV is much longer and therefore has a much bigger turning radius than a wheelchair. That's why they can be so difficult for newbies to drive and get hung up on corners so often. The rear of an ECV is wider than the front which throws many newbies off.
My last trip to EPCOT I was in Finding Nemo when I encountered a perfect example of what goes wrong in a narrow queue with an ECV. (Caveat: I like driving thru the Nemo queue with it's dark, twisty turns. It's an obstacle course for wheelies. Provided I only go to it when there is no line. Just me and the pathway.)
I made may way (happily) through the first section of twists then stopped dead in the second as I encountered a lady in front of me with a broken ECV. It was a rental, which are notoriously overused and prone to breaking. Poor dear tried and tried to get her ECV working again. Her family helped. The CM on duty tried to help. Thing kept beep beep beeping at her. (Mechanical issues.) Behind me were three other ECVs and a manual wheelchair followed by about 100 pedestrians. Now my powerchair is on the small size (22 inches wide) so I could squeeze around the broken ECV, but the other wheelies behind me were stuck.
Between my mechanically-inclined cousin and I we managed to get the broken ECV working and direct the pedestrians around us.
But the experience begs the question: what happens when you have an ECV broken-down inside Finding Nemo, TSM, Buzz or all the other queues that are really just big enough for a small wheelchair? Sometimes ADA regs are not sufficient for the situation they were written. (which explains why handicapped parking is pretty much useless for handicapped vans... most ADA regulated spaces are for car dimensions not vans with ramps)
I can envision one of the unintended consequences of DAS is that Disney is going to get a hard lesson in what should be considered an accessible queue. And exactly what do you do with a guest who cannot stand for more than 20 minutes, but you've told to get an ECV and then told they cannot use it in a 20+ minute queue? Not everyone can push themselves in a manual chair and not every guest travels with a party that can push them. So you let the ECVs into a queue not meant to accommodate them, one breaks down or gets caught on a tight turn and the WHOLE LINE shuts down in the sudden traffic jam. Or people start climbing over wheelies (which some do anyway) creating a moblike scene. So not pretty. That's when you end up with personal injury lawsuits and Disney at the heart of it.
The very worst queue for wheelies in WDW right now is IASW. This one suffers from that very circumstance of being too narrow to swing a cat or turn and retreat. After being caught inside it last March I learned my lesson to avoid it UNLESS I can get down to the very bottom unencumbered. Shame because it used to be a very easy to handle wheelchair queue BEFORE the remodel. People who design these things really should be required to go about the parks in a wheelchair and ECV themselves for a week first.