The German I/O module page has an animation which shows this in detail, it seems the English page is missing that for some reason:
The CSI and DSI pins are not accessible on external ports I'm afraid. I'm also not aware of plans to add modules which would make CSI/DSI available externally. In theory it's possible to open the case and attach wires to the pins which go to a connector external to the case and you could connect a CSI camera or DSI display there, however the result can hardly be considered "industrial". :-)
An alternative is to connect a USB camera.
The 4-core BCM2837 on the Compute Module 3 is beefy enough for image processing with OpenCV, in fact we're using OpenCV for our demos at expos. It may even be sufficient for video transcoding. One thing to be aware of though is that we're using a kernel with RT patches. Which means low latency, but also lower throughput. If you don't need low latencies but maximum throughput, it may be a good idea to use a kernel without RT patches. All the tooling to build a custom kernel is on GitHub.
I am actually working on a prototype of something similar- Pi, camera, small touchscreen, distance sensor and small number of IOs.
The two specific use cases for me: measure dimensions of parts hard to measure with other sensors and stopping conveyor when some parts end up in unexpected places.