Above is another example of a need for a “universal” video input. The camera that you are developing and tuning for the Pi will work for many people in many applications. But it won’t work for all people in all applications as cjowers7 noted above. He has a need for a very close focus distance. My particular application requires a camera with an analog / mechanical zoom lens. Thus sometimes the need arises to use a different camera.
As I explained before, camera modules are all different. So there is no such thing as universal input for them. The CSI-2 protocol doesn't dictate the protocol I2C needed to talk to the cameras. And the pain I am having just trying to get high frame rates out of this 'standard' camera is a prime example.
HDMI could be used as a universal video input, it needs no other interface than itself. But camera modules that output HDMI are unheard of - it's just not possible to make them that generic. So the problem of a generic camera interface is not as simple as implementing HDMI in. It's a currently unsolved problem i.e. no-one, anywhere in the whole wide world, has ever solved it. Nokia tried with SMIA, but pretty much failed. So even two SMIA compliant cameras need different drivers and setup (although it does make them slightly easier to write)
Volunteer at the Raspberry Pi Foundation, helper at Picademy September, October, November 2014.