There's a guy in the UK called Steve Parry that does various high-end Brompton customs. He does I think do a Rohloff but it involves re-engineering the whole rear triangle to accept the wider hub and tweaks to make the fold / latching still operable. Kinetics in the UK offers bromptons with the schlumpf retrofitted if you wanted to find out more...
http://www.kinetics-online.co.uk/