It's still AT-SPI for wayland, the main difference is how screen readers grab keyboard input events.[0] I don't think there is a big difference from a toolkit point of view. I don't personally have experience with Wayland because most blind people recommend Mate as being the most accessible desktop still.

Thanks for considering a11y for your toolkit - it really makes a difference to those of us who are disabled. Are you implementing a11y separately for each platform? If you use accesskit[1] you only have to implement it once for all platforms. I recently vibe coded accessibility for the Swell toolkit[2] used by Reaper. I have a branch using accesskit and a branch implementing at-spi. Accesskit made things a lot easier and more performant.

Let me know if you would like a screen reader user to help with testing your toolkit.

[0] https://lwn.net/Articles/1025127/

[1] https://github.com/AccessKit/accesskit

[2] https://github.com/RDMurray/WDL/tree/accesskit

and my fork of accesskit with some features and fixes for unix: https://github.com/RDMurray/accesskit/tree/swell-fixes