Long review time for pending changes is likely to be a significant contribution to user attrition on wikis where edits need review to go live (ie. on FlaggedRevs wikis which do not use "flagged protection" mode). While there aren't easy solutions for this (backlogs happen when the volume of new edits overwhelms the community's ability to review), it might be helpful to allow mentors to clear promising mentees' contributions quickly. That makes things easier for both the mentee (impact happens faster) and the mentor (reviewing a stream of somewhat trusted edits is easier than a mix of trusted and untrusted ones) and might motivate more people to do reviews. (This assumes the mentor has reviewer rights, but I'd assume that to be common.)
This could take the form of a column in the mentee overview table, with the number of pending edits shown, a link to the user's contributions (I don't think there's a way to list pending changes only from a user, but they do get highlighted in the list; given the typical mentee's amount of total contributions, probably not an issue), and some information about the time (max or median) their contributions have spent in the review queue: