Yeah, the threaded rod is only 5/8" diameter, so its not the right size. I had to 3D print an insert for each side to make up the difference between 5/8" (about 15.9 mm) and 20mm. If you're going to bother getting 20mm through-hole wheel hubs, you should use the right size bolt. In any case, I'd be surprised if you could find threaded 20mm rod, especially for as cheap as the 5/8" rod was.
Also, its much better to use a bolt that is mostly smooth and not threaded over its length for this, so you get a better interface with the bearings inside the wheel.
No, I haven't stopped working on the trike - we bought an RV trailer this summer, so most of my weekends have been spent away from home. I'll be getting back to this soon...