Thanks for the patch, there are few required changes though:
- Skip loop if no vert is selected, not faces.
- Move all the RNA_.*_get functions outside the for loop.
- Make a convex hull among all the selected objects, not one per object. (to be added to the active object mesh).
This probably requires a big refactor, so don't bother with this if you don't want to.
- Change totfacesel to totvertsel
- Move RNA_*_get functions outside the loop
Didn't try to make it create one convex hull for all the objects, I don't think I am familiar enough with Blender code yet.