I've hit #53984 and i'm interested in contributing.
I've tried to get started myself, reading the rustc chapters on new/old style trait solving and reading through the source, but didn't get far enough to understand what rustc actually misses.
My guess would be, that this falls into the realms of "Projection Equality".
I don't know if this is the right place to ask, but Is this a known limitation / are there resources available on this? How would i start with this?
I can't answer your real questions, but I think this is a reasonable place to ask!