Your later point is what makes me think this doesn't have comprehensive legs, just niche usage.

A typical game has thousands of hand placed nodes in 3D space, that do things like place lights, trigger story beats, account for physics and collisions etc. That wouldn't change with Gaussian splats, but if you needed to edit the world then even with deterministic generation, the whole world might change, and all your gameplay nodes are now misplaced.

That doesn't matter for some games, but I think it does matter for most.