Here is a scenario I encountered as a volunteer mentor:

1. I write a message at one of my mentees' talk page.
2. I ask them to write back to me, with a direct link to my talk page
3. as there is a [reply] button at my mentee talk page, the mentee uses it.
4. the mentee is not aware of the principle of mentioning others, so I don't get a ping
5. because I have hundreds of mentees to take care of, I don't watch the mentee's talk page. Or just because I'm off for a couple of days, I won't spot my mentee reply on my mentor dashboard

Consequence: I miss the message and the mentee is not happy that I don't reply.

Have a way for mentors to be pinged would be helpful.

Related (and inspiration): T272146: Automatically ping newcomers when their question has been answered.