I'm not aware of any plan to incorporate programatic costraints into Solvespace. I've given this a little bit of thought before, and I suspect it could be best done with a scripting language tied into Solvespace, in the style of Blender.
There are vague plans for integrating Lua in a way that lets people implement new constraints without touching the C++ code, but the current architecture makes it very hard. We're refactoring it but it will take a while until such scripting is viable.