When I was ruler I created a specific message group that combined new players and mentors. It came from the idea that a "group-learning" mentality might stimulate new players to ask questions freely, and join in conversation with other players (mentors), as well as allow them a "sandbox" mode to test out various kinds of messages, roleplays, ...
In Morek, since my ruler char is hero and can't be mentor, we created a guild for the purpose of welcoming newbies and teaching them stuff, much like the channel you explained. Newbies are invited to join the guild in the welcome message and ruler bulletin, many actually did, but there was always little to no interaction. I can easily found to be guilty, and complaining that newbies don't answer is not really a good defense, but frankly I can quickly lose interest or simply forget to keep in touch with newbies if after the initial 1-2 messages nothing comes back.
I agree that IRC gives a good environment where to learn things. I think it's pretty much established by now that while it gives a great rp ground, IC mentoring doesn't work as well as OOC one. Therefore creating a mentoring channel or something similar with a restricted amount of people allowed (if newbies join the main channel they will just get lost in the spam) and links to it within the game could be cool.
Also, I have no idea how the interface is for newcomers, but perhaps having them some sort of newbie standing orders reminding them a couple points of the game every time they log in could be good as well. (something like remember to interact, remember to write to mentors, join irc if you have questions blabla)
I don't know who's the mod of this channel, but to avoid repeating what was proposed before (like Vellos stressed) we should make a list of the most reasonable and agreed upon points for mentoring revamp and present it to the devs. I believe there are good suggestions in this thread already, and would improve considerably with some data from their part. I don't think they have the time to surf through such a long post thoroughly, let's help them.