I have a concept in mind, but have no idea yet whether it's going to work out: My idea is to require relationships between geometric objects to always be explicit.

For example, you're not allowed to define a point that happens to lie on a surface. You must instead explicitly define the point in terms of the surface. By extruding from a sketch that lies in the surface, or by saying "extrude until the shape hits the surface", or by specifying some kind of constraint.

I hope that it is practical to design CAD models in a way, such that these relationships are always explicit, and I hope that this will enable the CAD kernel to not have to rely on messy floating point stuff comparisons. But as I said, not no idea if it's going to work out like that.