Today all ECVs are left in the front of the mansion off to the side, any person using an ECV that can't walk on their own must transfer to a wheelchair.
I doubt this will change even with the new elevator no matter its location as there isn't enough space for them inside the mansion.
This is not accurate. ECVs and powered chairs can be taken down to load. CMs encourage ECV and powered chair owners to park them; but, if guests are not able to stand and make the walk - they can take them down. We've done this hundreds of times.
As the video shows, the infrastructure to use the path to the portrait corridor is already there and the only issue are the stairs.
But even foregoing all of this... loading ADA at one physical location and exiting them at another location would require some method of conveying the guest's method of transportation from one point to another within the roughly 8 minutes it takes to complete the circuit.
Doing so would require a separate stop of the omnimover per each "group" of ADA guests at the conclusion of the ride. This doesn't mean 1 Doom Buggy only as depending on group sizes, they can load multiple groups of people in chairs/ECVs. The most I've personally seen is 5 Doom Buggy's with 3 ADA groups of 1-3 people. When it stops at unload, the options would be load another group of ADA guests at load or send the current ADA lead buggy (130) around to load and stop again. While they could certainly reprogram the attraction to have a variable "ADA" lead RV, logistically it would be another deterrent to just using the almost ADA compliant cooridor path to exit that is just missing a ramp or elevator to work.
DL's Mansion only allows one ADA "group" on the ride at any given time because of the current issues with only being able to enter/exit from one point - load. I don't anticipate that changing. Again, the issue is the very challenging internal paths in the show building when trying to evac someone who isn't very ambulatory. Keeping everyone grouped together makes this much easier. In Florida or Tokyo, because entrance and exit are at ground level they have more options in the event of an emergency evac as all the emergency exit doors take you back to the same ground.
The unique ADA chair Clam on Mermaid certainly would help those that can't transfer; but, what is really needed are rides like the Kuka RV system or even TSMM or RSR that can call any RV into a separate load/unload station where it can take whatever time is needed without impacting the rest of the RV's in motion.
Even if Mansion had such a system, it wouldn't solve the problem that this solution that was announced for the reconfiguration of the ADA load/unload. This problem is addressing the challenge of getting TO the load/unload platform and not the process of loading/unloading. If a Buggy could be pulled out of rotation without stopping - it would still need to leave the track system far enough to then get to a lift of some sort to get back and forth to ground level. That type of complexity would require a complete redo of the very simply conveyor belt omnimover system that was created as a simple solution to keep the RVs moving. It accomplishes this by tethering them all together and pulls them as one.
BTW - I can't imagine whatever solution they come up with for the backstage hallway/path being too complex. The space available simply won't allow for much as it still has to serve as an emergency exit for all the guests at load level. For this reason, the stairs will need to remain or be replaced with a ramp; but, adding an elevator for ADA makes the most sense. Remember all of this is an excersise of space management. DL doesn't have the Florida Project's curse of space that is not being used.