I simply love Bike Forums, so many replies in no time! Thank you all.
@MassiveD: I used to run disc/v-brake combo, but during our winters you get to clean a lot of slush from the brake pads just too often. Plus now I nearly always ride with my two kids, that means too many kilos in the rear. It's very comforting to know you have reliable brakes descending from the hill on a wet day.
Apparently there is no suitable production frame, so I will probably go the custom way.