A little food for thought from someone who has to keep an eye on the video industry:
To date Sony has sold about 38 million consoles, but the second-biggest selling game to have the confidence to release actual sales numbers was Bloodborne at 2 million copies. Compare that to, say, roughly half of Wii-U owners having a copy of Splatoon. I wouldn't doubt a few other titles have sold more since, but the fact that nobody's willing to throw those numbers out to the public suggests sales for even massive AAA hits are still to a fairly small part of the overall userbase.
Everyone at The Escapist thinks of the PS4 as a downgraded PC, but the average consumer who buys a game or two every year thinks of it as an upgraded home theater product. Netflix and YouTube streaming apps, DVD/Blu-ray playback and connectivity to social media are the day-to-day functionality, with video games almost a secondary concern to be used on weekends or when a friend brings something new over to show off.
You see where this is going?
Those fancy 4K "Ultra High Definition" TVs have been out for a couple years now, but the actual spec all of them run on has only now been settled. BT.2020 is a lot more than just higher pixel counts - the High Dynamic Range colorspace behind it is a dramatic improvement over even digital cinema releases, and it features 10-bit video as standard to eliminate things like banding. This is awesome stuff for videophiles, and coupled with the HEVC codec, you could make digital streaming files smaller while maintaining (or even improving) quality on HD content.
The problem, aside from the TVs themselves not being BT.2020 ready (a cluster in and of itself, but irrelevant for this discussion) is... nothing out there really supports UHD playback, aside from a handful of specialty players that are little more than custom-built HTPC being sold at a loss. None of the GPU manufacturers out there are throwing in support for HEVC/UHD because none of the studios had agreed what UHD "was" until very recently, which left everyone in a holding pattern. Nobody wants to make new hardware that won't work with the new format, but nobody wants to use the new format if there's no hardware... and on it goes.
But 4K is only half of it: If Sony's going to overhaul the GPU for UHD compatability, that's going to require a lot more horsepower than what it has under the hood right now. The fact that they could use that excuse to dramatically improve what their Playstation VR support. The demos they've shown so far look fun, I'll give them that, but they also look like high-rez PS2 games with unique interactivity. If Sony wants to sell the PS4 as something you can strap a headset on and then play Battlefront or Assassins Creed or whatever in first-person, they're going to have to overhaul the hardware drastically to get even PS3-level quality running an inch from your face at framerates that won't make users vomit.
Will it make most games magically run better if a "PS4K" comes out? Nah, not really. Framerates will probably stabilize out on most games to whatever the target was, and I'm sure it'll upscale everything up to 4K, but this just means "Uncharted 5: You Didn't Think We'd Give Up Did You?" can be a 30fps "4K" title, with less refined shadows and post-processing than 1440p titles that are coming out the same week. By then AMD and Nvidia will be making cards that outpace the hardware, and we'll be back to about where we were before the PS3 came out; it'll be a comparatively powerful, but expensive and hard-to-sell beast with a handful of really cool exclusives, and a lot of functionality that kinda' sorta' works but will be made irrelevant quickly.
We've been here before, and we'll be here again.