While Stack Overflow is a great site, it is meant for specific programming questions. From the official help page:
What topics can I ask about here?
- specific programming problems
- software algorithms
- software tools commonly used by programmers
- practical, answerable problems that are unique to software development
Certain questions (that would be accepted here) would be considered out-of-scope/off-topic on Stack Overflow. Examples:
- What advantages does scanline rendering have over raytracer rendering?
- Are there any advantages for graphics cards that use shared memory?
- What exactly is a "GPU Boost"?
One of the main benefits this site would give to the Stack Exchange Network is that you could ask hardware specific (gpu) questions, while bridged to graphics programming topics and all under one site. If this site didn't exist, you could ask graphics library questions on gamedev; image processing on math or mathematica; computational geometry on stack overflow, gamedev, or blender; ray tracing on stackoverflow; and gpgpu on stackoverflow (although there isn't a great user-base for this on there). So, for experts in this field, they would have to participate in 3-5 sites and there would be no place for gpu specific questions or benchmarking.
To summarize, the addition of this site would create a place for graphics programmers to answer/ask questions related to their field and would create a place for asking questions related to graphics cards.