"They just work" is a surprisingly important start. FreeCAD improved a lot with it's latest release, but it still has many flaky gaps. Caps / apices are especially hard.
Higher order continuity native to the blend would be a requirement for many, too, and the algorithms only get harder and trickier to verify correct.
Higher order continuity native to the blend would be a requirement for many, too, and the algorithms only get harder and trickier to verify correct.