The Sigma TS-81 tripod socket is now shipping (check US pricing):
We are pleased to announce the availability of TRIPOD SOCKET TS-81 that is the optional lens foot which can be attached to the SIGMA 150-600mm F5-6.3 DG OS HSM | Sports. It is compatible with the Arca Swiss quick release plate and the clamp. The deliberately designed length of its rail provides the flexibility to adjust the center of gravity making it balance perfectly, even while zooming or using accessories, such as a tele converter and battery pack. Consideration has been given to the portability and transportation of the lens when Tripod Socket TS-81 is attached. The lens hood can still be reversed and the lens stored in its original padded case, even with the Tripod Socket TS-81 attached. Incorporated into the Tripod Socket are safety stopper screws to prevent the lens from falling. There are 2 sizes of screw holes, 1/4 and 3/8, making it compatible with tripods other than Arca Swiss, too. When it is compared to the supplied tripod socket, it offers more space between the lens and device, and the change of grip has improved the usage as a handle for carrying. (Sigma Japan)
The Sigma BG-11 base grip is also now shipping (check US pricing):
We are pleased to announce the availability of BASE GRIP BG-11 designed for the SIGMA dp Quattro series. When it is attached to the screw hole on the bottom surface of the camera, it allows handgrip-style of shooting. It is compact and convenient and therefore very easy to carry. The bottom part of the Base Grip BG-11 has a screw hole so that it can attach directly to a tripod. (Sigma Japan)
Sigma UK announced that the Sigma dp0 Quattro will be available in the UK towards the end of June at the suggested retail price of £899.99 (check US pricing).