Here's an interesting comparison of two masterings of "Onibaba" with pictorial examples. The comments on "superwhite" are interesting. Their assertion that the master that doesn't range out of 235 is doing a good thing is slightly misguided in my view even though they actually view it as a positive attribute of the master that does range above 235.
In trawling about I find lots of blunt assertion from pro/semi pro practitioners that video is 16-235 and everything outside that is "illegal". However if you read the standards for rec.709 and bt.601 what they continually state is that 236-254 is defined as headroom/superwhite/excursion.
(rather than just latching on to the obvious numbers 16-235 which is where I think a lot of this confusion stems from...people like absolute numbers)
Even if you ignore the fact that YCrCb maps higher into RGB and look just at the numbers in the spec sheet the chroma planes range from 16-240.
So that leaves us with 3 possible conclusions: ( this is referring to where the values end up on your display visually)
16 is black 235 is peak white and anything else is a bad thing.
16 is black and 254 is peak white and you should show the lot.
16 is black and peak white is 240 because the chroma planes range above 235 ( ignoring the mechanics of how YCrCb maps into RGB..someone else can do the maths I tend to fall asleep...I can't help it).
Last but not least what does this mean in the real world?
Watch some material with your display setup for peak white at 235 and then watch it at 254 and see what you think and post your observations.
I'm sure we can manage to do this without having a massive punchup if we remain a little open minded.
Things we think we know about video:
ideal display gamma in a dim environment 2.35
(assuming a range between 2.2-2.5 depending on viewing situation and display performance)
(B/W notionally justifiable as D.54 from a preferential/historical perspective)
Gamut... (according to standard and display capability and metering/adjustment capability)
white... see above (personally I'm sticking with 254 until I'm persuaded differently)