Improving the engine/physics/renderer fundamentally tends to break compatibility with existing game content.
Ideally, someone could fork, let's say NBlood, reworking the wonky physics and getting rid of the RoR graphic bugs and limitations. Older mods and episodes will have to be ported to the new engine.
Similar to how Nevander "remastered" Doom 64. He created a mod for GZDoom called Retribution that semi-faithfully recreates the original physics and map effects using scripting and uses many spiffy GZDoom features ... and then started porting the original episodes and unofficial mappacks over to this new "engine".