Aren't gaussian splats incompatible with most common game development styles? No shadows, no rigging/animation as main issues - or maybe I'm misunderstanding / behind on the research - please correct me.

You are right, that many features in game engines cannot be used yet, especially relighting and reflections. But there are cases where game engines (like Unreal Engine 5) are used, for example in Virtual Production with Ledscreens, where a photorealistic background is needed (3d gaussians do look more realistic and are cheaper to produce than a comparable scene made of polygons)

Supersplat is actually a game engine (but for the web)

This looks like a promising tool to (also) generate completely generative 4d Multiviews which then can be used to generate 3D-GS, their pipeline also supports animated objects, camera zoom and pan. They do benchmark their results with 3D GS. The code is unfortunately not yet published, cant wait to try it. https://gen-x-d.github.io/