I don't mean mentoring someone to be a programmer or a cook or a parent. I mean mentoring them on SE itself and how the system works. Here's how I would expect it to work (no idea how to implement it):
Two humans would communicate in some non-SE way (talking in person, for example) and agree to do this. The mentor would go to the protégé's profile and click a button, or vice versa. This would light up a button on the view of that profile seen by the person themselves, and send them an inbox notification: "Kate Gregory has offered to mentor you" or "Kate Gregory wants to be mentored by you." The person could accept the offer by clicking. (Or perhaps the button is on my own profile and I have to enter a user number. Something like that.)
And yes, I have to have a way of saying I will never mentor anyone or don't want to be mentored so leave me alone. Skip that for now, ok?
So then what happens is the mentor gets another pair of topbar buttons that use a different colour scheme. These show all the notifications the protégé sees, and have their "seen" status set only when the mentor sees them. I can notice that my protégé is getting comments, upvotes, downvotes and so on. I then interact with my protégé using some external mechanism (like going and talking to them, or emailing them) to advise them about the specific situation that is happening.
I think the coding effort on this is minimal since it leverages the topbar notifications. For those of us with time to take someone under our wing, it could make life far simpler than stalking someone's profile or visiting their questions and answers to see what is happening. Since the info in those notifications is public anyway, there's not really a privacy concern. Personally, I'd use it with people who I am recommending SO to. If you were concerned it would help puppets you could require a certain rep level to be a mentor. Heck, it could be a privilege to give out at a certain level.
If you were feeling super generous you could notify the mentor of things no-one is notified of yet: flags, votes to close, closure and so on that happen to posts by the protégé. But even without that I would find it worthwhile.
What are the advantages compared to strangers commenting on posts?
- newcomers may not stick around to get their own notifications. If I get them I can contact them outside of SO and say "something is happening on that question you posted"
- newcomers frankly misunderstand comments from strangers a LOT. They come here and complain about it. I can talk to my employee or relative or friend through some other mechanism and explain what people are saying.
- the newcomer can feel they have a bit of a safety net and have someone looking out for them. While not everyone needs this, it can help some new users.