This works great. I'd just propose to change some of the naming and add a descriptive tooltip.

I don't think we need to say "Apply & Delete". Apply always implies that the non-destructive element is deleted and becomes the new default (modifier, constraints, transforms).
We could name the operator just "Apply All Shape Keys".

It generally applies the visible result of the shapekeys. So if the toggle for "Shape Key Lock" is used, then it will only apply that active shapekey.
Disabled Shape Keys are also ignored. I'd say this works as expected then.
I would suggest that the tooltip says something like: "Apply visible shape keys and delete all"