This is too long for twitter, and I'm busy pecking away at other things, but.
Cheap idea for relighting the increasingly popular cubemap/image based lighting solution. Just store depth/normal/abedo of each cubemap face, and relight N cubemap faces a frame with the primary light/update the skybox. As long as you store the/apply the baked roughness lookups into the mipmaps, and apply such to the final output cubemaps you use for lighting, you get a dynamically re-lightable image based lighting system.
True you can't use lightmaps (unless you update those separately, perfectly possible) and can't get those pre-computed multiple bounces, but some price has to be paid for dynamic re-lighting, and since you're just re-shading a few 256x256 targets (and very basic shading at that) it's not going to cost much, and you can use whatever pre-computed ambient occlusion you want. If memory is a concern one could compress the albedo and normals down to two channels apiece, I don't see the quality of such being terribly important before lighting is applied.
Just an idea for now, but it seemed promising enough. There's still the other issues of cubemap lighting, parallax projection and light leaking and etc. but that would be solved separately and is needed research anyway.