Asymetrical or L/R Shape Keys with the Mirror Modifier

Sort of two key points bring this together, I believe the first has been brought up before, but the second and main point hinges on the first.

1. Shape keys should have a left and right side like vertex groups, that get edited simultaneously.

2. Asymmetrical or L/R shape keys should work with the mirror modifier, just like how vertex groups can.

This is literally the only reason you would ever need to take off the mirror modifier on a symmetrical mesh (Which, you can't even do without an add-on, unless you had no shape keys on your mesh)

Especially since I frequently only realise I need to edit the mesh to facilitate a shape key, and applying the mirror modifier just isn't feasible, since then I'd have to symmetrise the mesh in edit mode, and that breaks the left/right vertex groups and shape keys. I guess if symmetrise didnt also symmetrise L/R vertex groups that would be okay, but it does, even if you lock them.

This is especially relevant for animation, rigging, where redoing all the shape keys and vertex groups just to add a few extra vertices to correct a bend just isn't feasible. Also useful even if keeping symmetry isnt relevant, as currently the way to make L/R shape keys is hacky and you have to redo it every time you edit one.