The Wayland protocol "lacks" some things "by design" in that they are not specified. However, this is not intentional omissions, not even under the guise of "security", it's stuff that simply hasn't been done yet.
The most promising work towards improving accessibility support in Wayland was the work done on the Newton protocol:
https://blogs.gnome.org/a11y/2024/06/18/update-on-newton-the...
Unfortunately, the project appears to have stalled. I think the Linux desktop just lacks important strategic investments, and this is one of them. For now, existing accessibility bus support in UI toolkits is mostly being leveraged. Some compositors (i.e. KDE's kwin) also can support some old X11 features used for automation/accessibility (i.e. XTEST works, although applications will need to be granted permission first)
The situation is somewhat similar for IME: There are a few protocols for handling basic IME/text input, but it's not really finished, and further work on text input protocols has stalled.
This is not an ideal state of affairs at all, and it is a major threat to the future of the Linux desktop. I doubt many Wayland proponents (of which I do consider myself to be one) seriously believes that shipping Wayland-only without robust support for accessibility or internationalization is really a good idea. It's basically only happening because progress on Wayland has been rather slow, for many reasons, a lot of which really aren't in the control of open source contributors or maintainers. However, at the same time, maintaining both X.org and Wayland paths everywhere forever is also not sustainable: with limited resources, there simply has to be a point at which the line is drawn. X.org outside of XWayland has been unmaintained for a fairly long time.
On the flip side, if anyone working on Newton or Wayland accessibility has any idea what anyone on the outside can do to help things along, we'd love to know. I really hope that one of the major investors in the free software desktop (Valve? Red Hat?) can be convinced to help shift some resources to this. It's one thing to have some software work somewhat sub-optimally (as is the case with KiCAD), but it's a bigger issue that users who upgrade to newer free operating systems may face a system that is not usable for them because of limited accessibility tools. Possibly a compliance problem for companies that wish to ship systems based on free software desktops.