Operator Modifier / Script Modifier

I think the addition of the Weld modifier is great, but there is a lot more single operations that would be useful in a modifier stack for a non-destructive workflow.

Example 1 (thumbnail)
I need a Recalculate Normals modifier, because after using a Mirror Modifier, my normals are out of whack. Right now the only option for me is to Apply the modifiers and recalculate normals by hand, which isn't ideal.

Example 2
Ability to use Custom Operators in a modifier stack.

Example 3
Need to make manifolds from 20 objects? Add a Remove Loose Geometry, Fill Holes, copy modifier to all objects and you are good to go.

Proposal
An Operator Modifier that can do any action(s) on a mesh. The simplest would be to have just a field with auto completion like in the search menu and be able to do just one operation.

Or a more general approach:
A Script Modifier that just has one field that links to a script file and executes the script every time something earlier in the stack is changed.