The official line you'll get is that MIPI CSI2 was designed for going a few centimetres across a PCB within a phone or tablet. The camera modules have passed EMC compliance with the supplied cables, and we have checked signal integrity at those distances under "normal" conditions (no MIG welders or other large sources of interference).
You may well find that it works at longer lengths, and some have reported 2m as working, but please don't complain if you get EMC issues or image corruption.
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.