About ten years ago, I was a happy Ubuntu user. At that time, it stuck fairly close to the GNOME stack, which is good for me as a blind user since GNOME is reasonably accessible and has a small but dedicated group of folks working on it.
Then Canonical significantly abandoned GNOME for Unity. While Canonical advanced Unity, wrote its own mobile-optimized interface, decided not to use Wayland in favor of its own home-grown solution, it to the best of my knowledge assigned one (one!) staffer to work on the accessibility story for all the greenfield stuff it was building. Sure, you could run GNOME in Ubuntu if you wanted to be a version or two behind. Also, sometimes you'd get something like GNOME 3.10 accessibility components shipped with GNOME 3.8, which worked 95% of the time, but when it failed it failed hard. I wish I could remember specifics, but at the time I was busy feeling like Canonical had basically thrown its non-able-bodied users aside. The only Canonical accessibility staffer I knew of was claiming that the goal was to only make Ubuntu LTS releases definitely accessible but no commitments for any in between. That completely disregards how the accessibility stack itself sees improvements, and sometimes things become more accessible by virtue of nothing more than using a newer at-spi/atk. Sometimes I upgrade GNOME not for the New Shiny(TM), but because GNOME 3.next brings accessibility improvements that will make existing apps more stable and usable. But you can't always just ship a newer atk with a GNOME release a year and a half behind, so telling me I'll only get accessibility fixes in 2-year increments when access tech changes about as quickly as any other is, well, short-sighted.
I'd really like to see Ubuntu make more of a commitment to accessibility in this or some upcoming (but near) cycle. If you can build your own custom desktop environment and display manager, then surely Canonical can assign more than a single person or two to improve the accessibility of all that new tech. I remember Shuttleworth writing a blog post near the end of 2012, claiming that Ubuntu would leave no one behind, and that it would be relevant to all types of computing. As a blind developer, I tried to constructively comment that not making accessibility a priority more than once every two years both left me behind and made Ubuntu less relevant to me. My comment vanished into the moderation queue and was never published. Maybe it wasn't the congratulatory pat on the back folks were hoping for in that post. Today I'm on Fedora and, while it isn't perfect, the fact that it stays close to GNOME makes it significantly better for me. All your new tech can be just as accessible, but it won't happen if you make it a single person's job to do that work. And, if you can't make it accessible because of limited resources, then you are leaving people behind and might want to scale back your efforts in other areas to compensate.