Well, the function should be in the block editor. So it doesent have to be an Xref. Just a block in Dcad.
So you could even start drawing in dcad. For ex, draw some lines and make them a block.
Next go into blockeditor and launch sketchup to do some extrusion etc. Save in sketchup. And accept an update in Dcad.
This opens up some new workflow possibilities. I for one would probably use Dcad in an earlier stage of the project.
All these things can be done manually already. Export collada to Sketchup. Import SKP to Dcad.
However this sounds easy, it may not be easy to implement in DCAD.
The good thing is if this would work, in my case, I wouldn't feel the need for new
3d tools in DCAD. IMSI could just keep working on doublecad 2D. Not towards Turbocad which I don't think IMSI design wants anyway.