Promotional material is generally pre-rendered in which case the resolution is whatever the designer rendering the produced scene sets the render to, in-engine production shots are usually taken on development hardware that is using whatever pc monitor resolution theyre working on the title with, theres a big difference between target resolution and a resolution used when making the game (working environment), the idea of a promotional screenshot is to show off the game in the best possible light, what many people fail to realize is that many of these releases are done much higher resolution on purpose, questionable maybe, but also with today's print technologies, a higher resolution image bring provided as PR is done so with it in mind that it may end up in a magazines print, hence why PR agencies usually have logos in vector format or insanely high resolution CMYK png.
In all likelihood yes, next gen consoles may well ship with HDMI 2 and displayport connections, but again this isnt because the developers are aiming to run games at as high a resolution as humanly possible, the upper limit is still going to be 1080P, because regardless of how cheap 4K units will be at the time, the majority will still be using 1080P sets, and moving on from that, the hardware jump as i said would have to be the biggest hardware jump in the history of videogame generations to make the most of 4K, that just isn't going to happen.
The 1080p-4K resolution range is far too wide a gap for developers to push for targets within that range when they know full well the people that would benefit from it at the minority, and the gap is far too wide for a single generation upgrade to bridge, look at 7th-8th gen, it barely made the jump from 720p-1080p, and that's a pixel difference of 1,152,000, to jump up even to JUST 1440P, they would have to make a pixel difference jump of 1,612,800.
Its like the situation before the PS3 release when they were talking about how we would have 1080p 60fps games with thousands of players and so on, when in reality we got 720p or less and 30fps or less in most games, Sony were on the same overblown estimation you seem to have, the reality of that is even TWO generations since that claim, we aren't at a point where games are "averaging" 1080p/60, hell we're barely averaging 1080p/30
7th gen to 8th gen = higher resolution, more stable framerates
8th gen to 9th gen = finally stable 60fps at target resolution.
Once we get there though 4K will definitely be the next big step as by the end of the 9th gen, 4K or higher will be close to or already the standard, so the industry is going to have a major issue at that point if technology in home consoles continues its speed of progression.
Basically, your estimation of tech progress in consoles is vastly overblown.
Before the PS4/XBONE launched, my wife wrote a fairly detailed post about this, basically saying "if youre expecting 1080P/60 to be the norm, youre in for a shock", and the thread got bashed by people, just like you, who refused to believe the new consoles would be so underpowered, insisting that the magic of a closed box would make up for the low end components, but here we are, months after release, 1080p/60 is a bulletpoint in a small handful of titles with the averaging far from that, and with the way engines are progressing and the overall push, 1080P/60 is going to be the goal everyone would LIKE to hit, but wont loose any sleep over if they have to drop the res and/or framerate.
