[wrxtasy]

So in this case 720p stuff will trigger a format switch to 720p, output in native mode, and then allow the TV to upscale?

Yes.

Do you do this based on both horizontal AND vertical resolution (horizontal res >720 but 1280 or fewer horizontal samples), AND vertical (720 or fewer vertical lines) - to cope with letterbox and non-square 1280x1080 stuff? (If you just look at horizontal res the 1280 x 1080 could be confusing).

Or do you do a test after PAR has been taken into account (so 1280x1080 and 1440x1080 16:9 non-square stuff is seen as 1920x1080)

The code is mostly based on @Koying's SPMC Krypton work with a few small tweaks, the details of which start with commit #aoc8196 HERE (click)

I personally find this easier to use vs what is going on with the new Whitelist Leia refresh / resolution configurability.
Which for end users seemingly just adds a bunch of extra unnecessary complexity & confusion.