Okay, we went to Hollywood Studios today. We turned up at 10.05am with our FP+ and tapped ourselves in. We were amazed to see, once inside, that it was practically a walk-on! At the split I asked the girl on the gate how many people were waiting in the wheelchar section. She popped round the corner and returned to say that there weren't any. I then asked about the new third track. She said that you can take a wheelchair/
ECV all the way to the ride on that track. If you need special assistance (for a non-transferer out of a wheelchair, for example) then you'll still need to use the wheelchair side. However, I got right through and onto the ride at the third track with no problems at all - other than the fact that we probably ended up waiting longer in that queue (I think people chose to go on that one out of novelty as the queue on the first track didn't even reach the bottom of the stairs so clearly no queue to speak of there.
So, I very kindly 'took one for the team' so I could report back to you guys on ease of access for the new track. The cars are all very new, though, and the gun mechanisms are a bit stiff. I found that I wasn't firing a lot of the time as the knob didn't always go all the way in again between firing.