Sure, I'll try to elaborate on shader system later this or next week. Node based GUI would be great, too bad it's that time consuming.

After some testing here's a quick list of essential stuff that is missing (besides general stability).
- Render region - single most important thing missing.
- Per-camera dof settings. (Usually it's implemented via camera tag) Post render settings in tag would be handy too.
- Dynamic resolution with a lock button in liveviewer (in octane image conforms to the windows' size and locks render resolution with a special button)
- Physical sun&sky.

Material system is pretty confusing at the moment. I'd suggest to get more familiar with native shader building logic and try to get closer to that. Usually shaders are placed into standard slots and you get inside in one click, rather than 2 now. Both octane and vray are pretty well integrated into that system and it works great.

Also here's a little bug report.
When there's a shader effector in the scene - iterations are constantly interrupted thus render is stuck at 1-2 iterations and doesn't go further.
Scene file: https://yadi.sk/d/RMHV8NP0uX9Kc