Option 2 doesn't really fly.
CSI-2 is the interface carrying the data from the sensor to the GPU - http://www.mipi.org/specifications/came ... rface#CSI2
. It is a point-to-point multi-lane differential signalling link. I2C is used for the low bandwidth control of the sensor.
Muxing the CSI-2 bus whilst the sensor is running is almost guaranteed to be a non-starter. Stopping the sensor, changing muxes and starting may be possible, but others have already suggested it and it's generally been viewed as a tricky problem to sort due to the high frequencies, slightly odd bus PHY, and generally not being a particularly nice interface to work with.
The compute module will offer you the chance to run both cameras simultaneously. Syncing them accurately will be tricky, but many applications don't need the frame sync to less than a frame period (with a rolling shutter the whole frame from one sensor isn't being exposed at the same time anyway)
Software Engineer at Raspberry Pi Trading. Views expressed are still personal views.
I'm not interested in doing contracts for bespoke functionality - please don't ask.