Now we are talking, this is exactly what I needed 
Thank you so much for your detailed feedback!
1. Active Environment Export
During our initial testing, the active HDRI/EXR environment was set to export automatically (allowing users to select it under Custom Environment). However, it seems a regression bug was introduced recently. We are working on a fix and will release an update shortly.
2 & 3. Materials and Rendering Differences
Since the web viewer uses a different rendering engine (Three.js / WebGL) compared to Rhino’s native renderer, achieving 100% identical visual results is challenging. However, we agree that the metal material (middle sphere) needs inspection—it appears that the roughness parameter isn’t being applied correctly. We have added this to our issue/todo list.
4. Display Modifiers (Edge Softening, Curve Piping, Shutlining)
For viewport-based modifiers like Edge Softening, Curve Piping, and Shutlining, we can handle them by detecting these objects during the export process and automatically converting them to render meshes. We have added this feature request to our backlog as well.
Thank you again for testing and helping us improve the viewer!