>> The creator has also recently started working on a 3D modelling program (Dune3D) in the same style which I am very excited about.

I kind of wish he talked to us about doing a version of Solvespace using OCCT instead, but he's got a lot of good ideas and it will be nice to see where he goes with Dune3D. I can see its Solvespace roots!

Solvespace NURBS shells are completely separate from the sketch entities and constraints, so there's a fairly small API surface to make the change. That separation is also one of the issues preventing a fillet tool though.