>> Would it be worthwhile to consider switching to OCCT

It would, and it has been considered. The sketch elements in solvespace are significantly decoupled from the solid model. That means we could substitute (via wrapper maybe) an OCCT object instead of our SShell class. Then you'd have to change a set of solvespace curves to OCCT curves to make extrusions from them and such. But that would be most of the work.

We do tag all triangles in the mesh with a sketch entity handle for flat surfaces so you can constrain points to a face. I'm not sure how that would be handled. We will also be tagging edges of the solid with sketch entity handles in the future so we can do chamfers and fillets - say by selecting a line entity and applying a modifier to it which gets applied to the NURBS shell. I'm not sure how that would go with OCCT.

But yes I've given a bit of thought to it ;-)