Ioannis, I'm not sure why most manufacturers picked RS422 over RS485 since they both can go a long distance but it seems to be standard for the major manufacturers. Originally, they all tried to use their own proprietary networks but then they started selling their own brand of dome cameras for other manufacturers systems. For instance, the Pelco camera now has small adapter boards for each different brand of CCTV switch. My suggestion is to get your clients a bit more nailed down on what they plan to do.