Symmetry in local space

Is there way to have local symmetry planes,  either using a custom worklplane or whatever?

Currently symmetry only works on the World space.

Symmetry is not on world space. It is on object local space. You can use object pivot tool to set it.

Awesome!

Symmetry works to "mesh" pivot.

Use the object pivot tool(s) with caution if wanting symmetry position, as object pivot and mesh pivot are not always the same. Although the pivot tools can move both object/mesh pivot, any offset between object and mesh pivot will remain.

There is a tool for setting mesh pivot to base:- "Common modeling shortcut tools > Align mesh pivot to object base"

Yes, I do find the Mesh settings a bit redundant.   It is similar to how Maya works with all of the transforms residing on a null that behaves as the parent for the geometry (or mesh).  To keep it simple,  the mesh does not have any transform/pivot info.

Being able to symmetrically model in object space,  is really nice though.