Well, I managed to get a “dummy” export to 3MF from 3D Crafter. I say “dummy” because no matter what is in your scene it exports a cube. But that’s a big step. It shows the Microsoft 3MF SDK is usable from a 3D Crafter extension. I’m not sure how long it will take to turn a “dummy” into an actual exporter, but I’m guessing a week or two. Maybe less.