I think a good startup (I might even persue this idea) is a corporate-mentoring program that basically does code reviews w/ junior/mid-level team members esp - ones that maybe are having performance issues to go over code, or maybe even soft skills or productivity skills like communicating better or prioritizing and staying on scope.
The mentor would maybe take on 10 people in an org, and every other week go over some of their code 1:1 and offer suggestions, etc..
Basically Uber for Senior Devs (but only as mentors/training purposes).
Company could also help businesses build their own internal training systems to make juniors grow faster.