OK, I can see how complete integration would be quite tricky.
However, from a user's perspective, it would be quite sufficient if F360 (or other design tool) could launch Repetier host with the .stl output. Repetier host would in turn launch Cura with the .stl file. When user finishes the Cura save would be captured by Repetier. i..e. passing the files between the apps without actual integration.
No big deal, works fine now, just a nice to have.