Ah, sorry for double posts. Since a while there had been rumours that Sturmey Archer will produce a wider range 3 Spd hub extra for the brommi. Seems that on Eurobike one can get information on that (here a quote from Velovision):
"Brompton's wide six speed
A new wide-range three-speed hub from Sturmey Archer, combined with their two-speed 'derailleur' system, gives Brompton owners an extended gearing range - I'll have to nip back to confirm the exact numbers, but I gathered it was around the same as a wide-range cassette, or that of an 8 or 9-speed hub gear. It seems the hub is made especially for them by Sturmey. Didn't get any useful pics yet..."