While Disney is required to accommodate disabilities, they are not required to provide a guest's preferred accommodation. Since the majority of lines are wheelchair/ECV accessible and the very few that aren't give a return time for mobility device users, that's considered the accommodation for mobility and stamina issues. I fully understand your concerns, as I have back, hip, and knee issues myself, and sometimes have to use a cane but am still young and not ready to use an ECV/wheelchair either. I do know that day will eventually come though.
What made you think I thought they are required to accommodate me? I've already said that I don't have to go to Disney & won't, if my situation can't be accommodated in a manner that works for me. There are many vacation options. It's really not a big deal to me. Until this evening, I never thought about this situation. I do think it's wrong that physical disabilities can require you to pay extra, when other disabilities don't.
I don't know how young you are, but I was diagnosed with my autoimmune diseases at 27. Naturally, they've gotten worse through the years & caused a lot of damage to my body. I'm sorry you're dealing with it too. If you ever want someone to commiserate with, please feel free to PM me.
Something to keep in mind (and what I try to tell myself to prepare for my future need for a device) is it's nothing to be embarrassed about. Disney is far more walking than most people do at home and there's nothing wrong with using a tool to help keep you out of pain. You don't have to sit in it all day. You can park it in each land with the ECV/wheelchair parking and walk around when you're able. In regards to people giving dirty looks, well some people are just going to be jerks and there's nothing you can do to change that. The vast majority of people though are likely to be too consumed with staring at their phone or spending time with their own family to think twice about whether someone gets out of a mobility device and walks for a bit.
I understand what you're saying, but I'm simply not ready for that. I see no reason to use a wheelchair or ECV, when I can walk. Yes, I walk slowly & can't walk or stand for a long period of time, but I can walk. I can't climb stairs, but can walk a ramp or flat surface. I'm grateful for that.
I also understand why Disney does not offer a DAS for these issues. A DAS can involve more walking since you have to walk to the attraction to get the return time, then walk somewhere else to wait, then walk back again to enter the FP line. There may not be anywhere to sit as oftentimes the few benches are occupied and they sometimes don't allow you to sit at the quick service if you are not buying food. As a regular park goer, I'm sure you're familiar with the limited seating, but many others aren't. I could easily see the frustration some people would have with walking to get a return time to find there's no where to sit and then complaining that while Disney allowed them not to stand in line, they provided nowhere for them to sit outside the line. Since guest's tend to do far more walking around the parks (outside of the lines), and to the buses, standing in line for the buses, etc, none of which the DAS can accommodate, it makes sense that they recommend those who will have difficulty standing/walking in the queues to get a wheelchair/ECV as that really is the only way to guarantee you'll have a place to sit when you need it.
Couldn't my DH or DS walk to the attraction to get a return time for the 3 of us similar to the old fastpasses? We've never had a problem finding an out of the way place to sit & would have no problem buying drinks & a snack to have a place to sit. I'd rather throw the snacks away than have to leave the park, because the pain makes it impossible to stay any longer.
Also, there are unfortunately numerous people who have difficulty walking the parks everyday of a vacation for a multitude of reasons. People with back, knee, hip, or ankle injuries, joint replacements, plantar fasciitis, arthritis, osteoporosis, and so, so many other medical issues that affect mobility and stamina. People who may not require the use of a mobility device at home, but find that Disney requires far more walking than what they are used to or can handle.
If DAS were given out to all of these people, FP lines would undoubtedly end up being packed with people with DAS return times, making the lines even longer, as it was with GAC. Those using the DAS would be upset because the FP line is now 30 or 45 mins instead of the 10 that it is now, which would make it more difficult or impossible for many disabled folks to even wait in that line. The standby waits would also increase since more people are in the FP lines, which in turn would leave more people with requesting DAS accommodation because while they can manage what the lines are now, they may not be able to manage if the lines become significantly longer. It's just not really a sustainable accommodation from a park operations standpoint to provide DAS for mobility and stamina issues.
In all seriousness, that wouldn't be the reason I wouldn't get one, but it is a consideration.
Honestly, I wouldn't want one, if it was free. The thought that I would have to pay extra to enjoy the parks, when we're posting on a disability thread about people expecting to ride a ride multiple times, with no wait, did make me laugh. 
