An additional challenge is that, if I get a PR of which I don't like the specific way it's been done, I can patch it up myself. And if it's a feature I don't wa

An additional challenge is that, if I get a PR of which I don't like the specific way it's been done, I can patch it up myself. And if it's a feature I don't want added at all, I can already turn it down at the proposal stage, before any code is written. With UX, however, the contribution itself isn't the proof that the contributor actually knows what they're doing. I've been excited about getting a UX contributor in the past, but then with all due respect what they turned up with was even worse than what I could've done - and this was not just a matter of taste and expertise. But it's rough to turn it down after the work's been done.