This would make easier to make levels as the Stunt Rally editor is very easy to use. Obviously it would need to be adjusted to STK-specific stuff, but the basis is there for a good course editor.
Using Blender as a track editor isn't a good choice IMO. Let's face it - Blender has a lot of unneeded (and potentially confusing for someone who never used Blender and just want to make a cool SMK track) fluff, not to mention Blender isn't the most intuitive modeling program even when you don't have to abide to any arbitrary restrictions - I still don't know how to do half the stuff that is possible in Blender and I'm using it since 2.3x (2.37 I think, but not really sure), the constant UI changes aren't helping either.
With a dedicated track editor a lot of confusion would go away since the user would only have access to tools that are actually useful when making a track and couldn't make a track that is unreadable by SMK by accident (obviously making a broken track would still be a possibility but at least it would be only broken in gameplay terms, not as in crashes the game or looks weird, most likely due to flipped normals).