Why Seperate when you can integrate
I'm taking a stance, and publicly telling you my vision on the issue of separation and integration for safety and control. When this happens, is still up to debate.
I believe that one day it will only take one control system to automate your critical process. That's right, there will be day where it is commonly accepted that a single platform can and will provide both control and safety shutdown operations. The system themselves will be able to provide the logical seperation necessary to comply.
However, before this comes to fruition, it will take much work on system manufactures to provide a hardened platform that is both capable and reliable to take on this responsibility, and even more importantly plant owner/operators to have the diligence to instill complete safety lifecycle procedures at their facilities.
Some manufactures may argue they're already there.