Don't most sets bypass/disable their model specific on-the-fly tonemapping on content with HDR10+ / DV (dynamic metadata) content (so as not to tonemap it twice)? I always thought this was the case.
With those formats yes, they are both recognised standard HDR profiles as part of the ST2094 standards which both have their own tone mapping processes. HDR10 doesn't specify any specific image transforms to be used.
Soemthing like ABL , zonal local dimming or even just the rule of thumb of a display becoming dimmer as the window size increases is not accounted for in any format.
This new option on PS4 is one of the things being passed across to games which will help the content to maybe be able to take some of that that into account in a real time, dynamic manner.
So if you are playing say Killzone and it's bright daylight, ABL will kick in and bump down the entire luminance of the screen. You literally lose Dynamic range as the display tries to protect itself against overheating and burn in.
Now rather than presenting this very bright daylight scene which the game now knows cannot be displayed , the game can choose to reduce the luminance of the skybox but maintain the luminance of game critical visual information of say the enemy's glowing eyes, which are used as a by design visual cue for identifying enemies and maintain a high dynamic range image.
It's this type of application that they wish to achieve with this method which has been designed for games.
This inner knowledge of the content cannot be achieved using a display based post process tone mapping, certainly not to the degree that a game could do itself