Well...if you still have a 1080p TV, you should get a PS4 Slim or stick with the OG PS4 you already have.
If you have a 4K TV, and want actual 4K gaming, you should bite the bullet and buy/build a powerful gaming PC. The PS4 Pro will not be able to do true 4K in actual demanding games, it's all going to be tricks and nonsense like checkerboard rendering, upscaling portions of the image outside of the center, and other things which will not look that good.
If you have a 4K TV, and want 4K Blu-ray playback, well at this point you either downgrade your gaming experience with an Xbox One S or just sit it out until more standalone 4K Blu-ray players are available next year. Or you can buy that $400 Samsung 4K Blu-ray player which I heard is a kind of buggy.
So...I don't really know who this thing is for to be honest. I already played through Rise of the Tomb Raider in true 4K earlier this year. I'm working my way through Deus Ex: Mankind Divided in true 4K although it's on the shelf right now because the impending DX12 patch. Anyone who actually cares about 4K gaming already has a fire-breathing gaming PC.
There's the wild-card that is VR of course, but the jury's out on that. PC VR is having serious problems right now as sales have stalled out of the gate because of the idiocy of fragmenting a nascent niche market right away between the Oculus Rift and HTC Vive. PSVR won't have that problem but even the PS4 Pro is vastly inferior hardware to a VR-spec gaming PC so we'll see how it looks and performs.