I'd be interested in this as well. I'm thinking about getting an 8spd internal-geared hub on a Downtube foldable 20" bike, and options seem to be so readily available for this specific bike.
Let's see... I could hook the chain directly up to the freewheel in the back and have gears, but of course, I'd have to let off the gas to change gears, but this will prolly give me greater gas milage AND too much speed for a foldable frame. I could leave the chain on the pedals in tact and put spokes thru the engine's sprocket. Or I could get an electric hub with a huge battery, prolly making it still truly foldable. ??? I dunno yet.
I did the research, your search terms came up with better searches, tho. Either way... none of the threads were definitive about whether or not hubs with internal gears would work. Only the one that I linked to above had any hope, and sure enough... the guy posted pics when I asked, and it appears that he's been riding it for a long while.