Global Screen Reader Modifier
This was brought up in this Orca issue, #330.
There is an open PR that is currently blocked on an issue with the capslock (Orca modifier key) not being captured and consumed by the screen reader. @joanmarie has mentioned that this has always "been a sad hack with various bugs"; just in the time Orca has been on Gitlab, I've found a handful of issues related to this. 71 293 80 (although 80 looks like it's a dud).
Joanmarie makes a good point, and it shifts important, core responsibilities to a screen reader instead of having the onus on the desktop environment and accessibility infrastructure for basic functionality like a screen reader key (which as far as we can tell is something more-or-less universal for screen readers).
If there is support for this from @federico, I'd be happy to implement it myself. We'll also need buy in from other desktop environmentsL Mate and KDE should at least be notified.
I'm thinking something like set_screen_reader_modifier(keysym: int_32) -> boolean
; this allows for any key to become the screen reader modifier, but I'm open to arguments as to why this should not be the case.