Will Unity upgrade mono to 2.8+ for .Net 4 compatability?

Similar questions have been asked before, however none are up to date.

The current lack of covariance/contravariance support for generics is a pain.
Are there any plans to upgrade the mono version used by Unity, or is there a way to configure Unity to use another version?

No nothing is actually plan. And the core Mono version of Unity couldn’t be change. You can change the IDE but it will not change the Unity compile way.