Introducing a second HL library?

[Philippe Hurbain]

But how do you add normals to a missing surface,

As Nicola (I think it's him) explained, it's easy to derive normals from a smooth shading algrorithm. Only fine tweaking for special needs would have to rely on human intervention...

or connectivity information to a missing primitive?

Anyway you can't define connectifity only from primitives (eg. tile in minifig hand). It's a big helper, but not sufficient.