Okay that makes sense. If this works it would effectively eliminate the need to use my Lumetri preset (or like I do, record the footage incorrectly flagged as rec709) and would also eliminate the need to either use setparams, side data, or set the color space info directly in the encoder as well. It would save a lot of work for sure!
The only remaining thing would be setting the Max/Min MDL and MaxCLL/FALL metadata. You can get away with not setting it, but content will usually look better if that metadata is set correctly.
Of course I've already started a project using my old method lol, and premiere won't let me re-interpret the color space of my footage, so I'll have to wait until my next project to be able to make use of it for my own work, although I could probably do some quick tests.