Why are you thankful? Do you need accessibility, and if so, what do you use?
Inevitably someone complains about lack of accessibility of a custom UI toolkit, which is frustrating, because something that helps 99% of people is still an improvement and still worth doing.
The argument would be that a new GUI toolkit will capture applications that would otherwise be made with an older, accessible toolkit. In that sense, it‘s a regression, not just a clear improvement.
I do agree about the idea though. We shouldn't shut down experiments just because they don‘t have a plan for it yet. I do see some of that on twitter etc. But once you‘re shipping software that users can‘t switch away from, because of network effects or because it‘s at work, it‘s not ok.