ImplicitCAD, Libfive, Curv, and Descartes are all in the same family of signed-distance field modeling tools. Descartes is very alpha, so I wouldn’t call it as usable as the other three modelers.
The convex hull problem really requires a mesh for arbitrary geometries, but there are some simple cases for primitives such as hull of two cubes or two spheres that can be done in certain cases. A pure approach to convex hulls on arbitrary signed-distance/implicit functions is not something I have encountered yet.
On the other hand, SDF->Mesh->SDF is something I am exploring now for tetrahedral mesh generation, particularly targeting grid-like structures (level sets, DICOMs, etc). This should set the foundation for convex hulls. I strongly agree with you that programmatic solid modelers need the basic operations (filet, chamfer, sweep, hull) to be usable and no tool has all of these yet.
This semester I am working to finish up DistMesh and work on a Descartes → DistMesh → JuaFEM/TopOpt pipeline for parametric design studies. As for things printed with Descartes just look at my profile picture! 
It was done by decimating the Stanford Bunny and calling this function.