I am not a potential costumer becouse shipping cost would be crazy from where you are but I would say that the option to upgrade/ rebuild is important. My Curve is a three speed IGH. I know I can upgrade to 5 speed 28 h hub (as long as they can be forund) and a 8 speed hub.. Maybe the OLD and the option to easily install a chain tensioner or der is more important than selling it with 8 speed hub. If you buy a cheap(ish) bike with a good frame and several options for upgrading the gears It would be easyer to sell them I think. Ask if they can add that piece on the left chainstay that makes it easy to install a IGH with coaster but keep the option for other brakes.

If you read the forums the stems and headset is something peopel often worry about. Especially becouse they may want to remove the stem to put the bike in a suitcase. I would consider going back to a quill stem to be an upgrade on any folder for this reason. Much easyer for peopel to deal with both for maintanance and traveling.

Edit: Forgot to mention a crank set that makes it easy to change the gearing (chainring) without buying a new set.

After reading about the click fix breaking in another thread I looked at the new Dahon luggage and luggage system on your site. It looks great but the prices are "stiff". I would hope we soon see somebody making a strong good quality "closetotheframe" adaptor for Dahon to Brompton and Brompton to Dahon luggage so that peopel who own several folders (or buy and sell different folders) do not have to invest in new luggage for each bike. It is about available space in peopels houses and also about money. To hope for the option to get the Brompton weld-on on Dahons is much to hope for I guess...

This may not be what you asked for but this is what comes into my mind. I only buy things that have more than one purpose so knowing the bike is flexible both in gearing, packing and luggage is key IMHO.