ACES and Rec2020 are not just about brightness dynamic range but also about chromatic range/gamut. With the right display you will be able to see stronger more saturated colors than you could on a regular monitor or tv.
You can get an idea of this when you read about aces/rec2020 and see the horse shoe shaped color wheel with the different boundary triangles inside for comparisons.
So only lighting on old texture pipelines would not get you all that you can have for HDR displays.
Presumably like you suggest there could be a lut that can transform an sRGB’ish color space to something like the wider gamut. But you would loose bits of fidelity in both chromatics and luminance as you are stretching out colors and ‘bending’ out baked in luminance curves and clipping(rec709/srgb gamma and white points).
I assume like for all color work the better your source material the better the potential result. So if you had HDR/wide gamut acquisition and a non destructive pipeline feeding say exr’s as textures to Unreal then that should give you the best results. You’d probably want to have your paint software supporting this and a hdr display for the artist making assets.
Currently I am trying to figure out how ACEScg would be different from a regular old fashioned linear exr/data.