For any big planar surface they’d be essentially useless, but for things like bottles and shards of glass I think they’d be more than good enough. They don’t have nearly enough angular resolution to do much more, but I feel like it would be possible to pull something off with them.
To your point: https://www.youtube.com/watch?v=XZw5CXAJ2hg
Their implementation was so good I remember trying out HLA and thinking Valve had somehow snuck RT reflections onto a VR headset. It is so accurate and such an artful implementation I am blown away. If we had a better way to generate scene proxies for cubemaps in UE, I think they’d be far more viable than they are now.
So, get your PBR buffers, your normal, your depth, and relight that dynamically as opposed to constantly doing full scene captures? That is very clever! Although as the Mafia 3 presentation pointed out, certain scenes are extremely difficult for depth cubemap reflections to solve, such as anything with a lot of thin geo or occluders.
Please let me know how it goes. With the right implementation I feel like you could have something very performant, but given how tight lumen is already I’m curious what your numbers would be.