It is impressive... I toyed with the idea to implement something like that on mine, then decided against it as 10-sp chains are actually a lot more expensive than 8-sp ones. So on that I decided not to pursue it. I have other gearing option ready to go when I need them for loaded touring. For commuting, 2-sp all the way.
I recall you writing about a 5 speed hub but that there was something outside the driveside dropout. I've seen a few photos but don't recall anyone discussing the driveside thingy with respect to the fold.
Using Sheldon's calculator and the Sturmey Archer Brompton special wide three speed hub, 12-15-17 and 13-15-17 cassettes seem to produce a decent spreads. One would still have to do a double shift -- IGH and derailer -- to smoothly move up the gears; but I'd think that the additional range and choice with the rear cassette would make it less frequent.