I only had a few minutes this morning before I had to leave for work, but I made a short test. It works!
The setting is there and enabled by default.
My GUI setting is 1920x1080
720p (25fps / iplayer-download) is played as 720p
1080p (23.976fps) is played as 1080p
I had wished that SD from Live TV (tvheadend) will be played out as 576 (or whatever it is, I’m far from the Vero right now) but SD is played out as 720p according to my tv.
So all in all it looks like a success but not on all fronts. Thank you, Sam!