- external sync for sensor trigger (genlock, trigger master-slave)
- external sync for camera parameters (shutter, whitebalance, etc.)
- sensor position finetuning (backfocus, top/bottom & left/right shift in a "few millimeters" area), roll & tilt compensation is not required
- SDI output so the signals from both cameras can be converted into something 3d monitors can display with a device like this: http://www.aja.com/en/products/mini-converters/hi5-3d
The industry is still split between declaring DOF good or bad as esthetically element for S3D.
In general a 2/3" sensor diameter is considered the standard for reduced DOF Stereo 3D recording.