The mentor feature is basically useless, there are way too many people using Exercism for mentors to be able to contact each and every one of them. Your best bet is to just do the exercises themselves and search for any errors.
I haven't used it in a while so I don't remember the pain points but that seems correct. I was mostly interested in doing the exercises and not the feedback.
What I meant with my original comment was that exercism.io had the right features for providing student feedback already, i.e. the feedback was the main point of the platform.
This depends on the language path. I've been mentoring a few of the language paths, but as an opportunity to learn/use the system, I've also been a student on a number of them. Some are overwhelmed. For instance, there was an online course on Prolog earlier this year the seemed to overwhelm the Prolog track with a glut of new students. Other tracks have problems that are harder to mentor, the code is complex, so some mentors choose to avoid those problems creating a bottleneck. Their choice is reasonable, but without more experienced mentors the problem just gets worse.
Additionally, they're working on the third version of the site. So a lot of people are focusing their attention on that, or dividing their attention between making new content and handling the current load.
