Rating system for Safety Critical Systems based on various attributes such as Reliability, Availability, Maintainability, Etc...

We all know that Safety Critical systems are Categorized based on the Tolerable Hazard Rates (THR), which assigns them a safety integrity level (SIL). I think the next level of rating of these systems shall be based on the other attributes besides safety, since many products meet the SIL level but have different architectures and RAM data, this kind of rating will provide the vendors the comfort in choosing the right product for the environment they intend to deploy these systems. The main attributes that form as input to the rating criteria shall be:

1. System Architecture
2. Reliability
3. Availability
4. Maintainability
5. Historical Safety Record
6. System Complexity
7. Ease of Usage
8. Expandability of the system
9. Fault Tolerance
10. Cost
11. Cost of Maintenance Etc...