There are several 3D programs that have built-in direct upload to Sketchfab. I wish Rhino was one of them.
I know the folks at SketchFab have interest in this:
Perhaps you should post something on their site forum and give them a friendly reminder.
A community member recently built a plugin, maybe you could try it?
Sketchfab.rhi.zip (31.1 KB)
Thanks Dale and PadreZippo,
I’ll check both.