I bet there could be some accessibility-related use for the touch bar. Also, accessibility is already tied to completely unrelated things like event taps.

"Accessibility" is kind of the catch all super-permission to give to hooks into greater parts of the operating system.

For example, Dropbox requires it for some features, as does an App that hides menubar items.

That's also how keyboard remapping apps (like Karabiner) work, so it seems plausible here at least.