The fellow @ Loopwheels is up in full production. You can buy just the 20" wheels as an upgrade or a turnkey Dahon bike:



The hubs are Sturmey-Archer X-RDC and X-FD drums.

Don't sell the steak, sell the sizzle:

https://youtu.be/P5JPB_kKAg8

It seems like this is the sort of thing ThorUSA would be the US distributor of.