Ok. Looks like this upgrade is not optional which is fair enough. Interesting to see if it lasts as long. Shame as I was planning on reusing the spokes this time.
are you assuming or did you already talk to the Dealer ?
Brompton is all about retro compatibility , ask at the company , they respond to individual emails ..
I got a warrantee left pedal direct from them.
as to the spider crank , you may be able to use another 130 bcd road crank .
There is the option of Surly's Stainless steel chainrings up to 50t. very long wearing.