Sorry to piggy back on this thread, but keeping in mind what you've just said Tom, if we plan to capture and use backplates in render (rather than compositing in post) would it make sense to process our backplates with no tone curve applied, linear so to speak? The way I see it, if we use backplates in render then they generally already have a tone curve of some sort applied either in camera or in lightroom etc. ACES OT would then technically double up on this tone curve. So if we can't cancel the ACES OT transform out, then perhaps starting without a base tone curve on the backplates would be the next best option? Of course this is only possible if we're shooting our own backplates and/or have access to the raw files?
We often shoot 360 backplates (not HDRI's) on site and use them in render for both direct visiblity and reflections, but there is always a battle trying to get it to look right in render, without any additional colour transforms/brightess changes due to the issues you've described.
Disclaimer - I'm not technical, I could be way off here
