I knew this would come up eventually
Unfortunately, there isn’t a clean and easy way to differentiate between the two (both geometrically in Speckle and for different use cases) and so far, converting to acad 3d polys when all segments are linear has been the most flexible catch-all strategy.
It would be easier to preserve 2d polys in the autocad ↔ autocad workflow as it’s fairly easy to add an
Is2D property, but in the case of a 3D platform like Rhino to a primarily 2D platform like Autocad, you’re essentially asking to by default remove a dimension of information, which isn’t the most robust assumption (especially since we anticipate most workflows moving 2D > 3D > BIM / Vis).
For now I think you’ll just have to manage with 3d polys from Rhino: we may add platform-specific user options to our UI in the future that could provide a 2D toggle in autocad, but this would be quite far down our development roadmap