If you are unable to make a gray level prototype with BSP, then that would be a problem. But building a complete level that way and trying to get all your detail is not a good workflow, there’s so many things that you would need to be able to do that you wouldn’t be able to even if they improved the modeling tools. The 3D programs available already do a much better job, there’s no sense in development on trying to replicate them when other things are far more important.