I'm sorry if it this has been cleared up, but I haven't seen any announcement on whether the pro will be able to force down sampling on 1080p TV's.
For all we know it could be 4k TV detected output 4k, 1080p panel detected output throttled down PS4 mode until a 1080 enhanced patch is available.
what makes you so sure 4k content will be automatically downsampled?
Edit: Apologies, looks like J_ToSaveTheDay got to the crux of this earlier in the thread.
Let me break down what your saying:
"For all we know, it could be 4K output to the TV and 1080p down to PS4 'mode'?"
But that does not make any sense. 4K output is essentially enabled by default for every PS4 Pro game as long as you have a 4K TV, because it supports the HDMI 2.0 standard. The same is the case for the Xbox One S and any 4K output enabled device.
Furthermore, if 1080p output to 1080p TV's goes down to this supposed base PS4 mode, then what exactly is the 4K output enabled mode if you say there are no changes to the game otherwise?
When Tabata and other devs talk about "4K", unless claimed to be native, they are referring specifically to checkerboard rendering mode, which means that they have a higher resolution they are reprojecting out to 4K using checkerboard rendering. This is the resolution that will be downsampled to your 1080p TV.
Developers having a '1080p enhanced mode' should only be considered if the developer themselves state that they are adding such a mode.
I've said it before, the PS4 original game is essentially out of the picture. If a dev has a singular pro mode, that will display on whatever TV you have, it will not disable.