I agree that It would be nice to have a super simple, "unrealistic" fog mode. Maybe a specialized medium like 'simple absorption', 'simple scattering', etc. so that it's more or less compatible with the existing workflow.
Fog is one of the 3d techniques that's been around forever, and even when it's done in a very simple and efficient way, looks extremely realistic. In many cases, simple distance fog is more than adequate. It's been available in real-time rendering for almost 30 years. What Octane provides is far too slow in many circumstances.
There are many projects that I can't use Octane because it can't handle simple environment fog in a practical way, like the ancient Max Scanline render can.