The idea is here :
i think the only way to boost 3DGS rely on people like you matt ;
caus in fact you create additionnal system to 3DGS core that are.

additionnal scene management could only be benefic, octree : not easy perhaps to implement ?

perhaps you could put a new light management with shadows like Frank_g requested ?

I think the future for 3DGS enhancement is like ogre3D : powerfull dedied plugins !