[dTal]

>Even if someone did want to help in this role, the developers on most projects would probably ignore them.

This is the lion's share of the problem, I suspect. OSS projects are driven by the people who write the code, and they don't take orders, and they don't massively value making things easy to use - or even necessarily have much connection with what that means. Current computing is such a pain in the ass that we've basically selected for inhuman levels of persistence and patience, and placed a large cultural value on those traits to boot. "Read the docs", we say. "Use the source", we say.

We don't have any idea how many human factors experts are out there, willing to help, because there's no process for them to contribute beyond "submit a pull request" - and even then, a purely UI tweak will meet with huge resistance. The UI expert is going to have to be a diplomat as well.