[Pierre-Marie Baty]

It's not that simple.

The capabilities of the engine when it comes to rendering a certain type of environment are tightly tied to the way the data is stored and exploited. It's at the base of what makes an engine works.

You can't "fix" a BSP engine to render outdoor environments better, because it'll still be a BSP engine, no matter what you do. You can't change the way it works, else better rewriting a new engine from scratch (with no guarantees to do better than the existing).

Identically you can't "fix" an outdoor engine to render indoor atmospheres nicely with all the shadings, because for the engine there's no difference between an indoor and an outdoor environment. It's all about rendering polygons and putting them in a certain order, and then applying formulas on each of the pixels. The engine doesn't give a sh*t if it's a "room" or a "valley" or a "corridor" or a "mountain". Clean indoor shadings require a BSP engine, and it's not what the outdoor engine is about.