ReallyRightStuff now has the Modular L-Plate and grip system for Leica M8/M9 available for pre-order (see original post here). Shipments will start in June, 2010:
The replacement base plate completely replaces the Leica base. This replacement base has an integrated dovetail for mounting in a Really Right Stuff clamp. Use the base alone as a conventional plate, or add an optional vertical component to create the L-plate, or add an optional grip. Both vertical components screws precisely to the base using the included hex key:
More pictures after the break: