New gameplay mechanics are infrequent in the same way new discoveries in scientific fields are infrequent. Once areas of research are mature, you get evolution rather than revolution. It probably doesn't help that controllers have largely been the same for three generations but increasing the power lets developers remove barriers. Like how AC Unity has a seamless game world where you can roam from outside to inside to outside again. With insane amounts of detail. Skyrim had loading zones for cities but on a decent PC you can mod (Open Cities) those out and have all the NPCs interacting at once. Does that change gameplay? Yeah, because now things that happen outside the city create a reaction inside the city. It's dynamics that were not possible before.
Is anybody doing anything really groundbreaking? I don't know, sometimes it's really hard to tell what is going on under the hood. Shadow of Mordor has the Nemesis system which just couldn't be done on the 360 and PS3. More NPCs, more physics, better animation, more dynamics, less canned stuff. Some of things that I see in GTA V still surprise me and it happens because Rockstar build a complimentary suite of game mechanic systems that are logical, environmentally adapting but not predictable.
Increasing the performance means being able to solve problems that create immersion breaking issues. Crackdown 3 may run offline (and better) on Scorpio compared to their promised cloud-solution for Xbox One. Lacking performance means compromising somewhere.
Skyrim is officially supported on 2008 era hardware. Shadow of Mordor is officially supported on 2010 era hardware. Both will run on lower hardware than is actually supported. Those are both examples that boost the viability of a rolling generation of hardware.
Your Skyrim example enhances the gameplay experience, much like graphics, but it doesn't change the gameplay in anyway. All it does is remove the loading between some parts of the game. You could likely achieve the same results with a better stream solution as other open world games games which run on previous generations of hardware could do.
The current generation version of GTA V is officially supported on 2008 era hardware. While the graphics change, the gameplay doesn't. GTA V would likely run even on 2004/2005 era hardware by further scaling down the graphics. Oh wait, it does run on 2004/2005 hardware with exactly the same gameplay when you scale down the graphics.
From a non-graphical or convenience (loading zones) POV, you could run pretty much every title released on current gen consoles on 2008 era hardware. And with very rare exceptions you could likely run every game released for current gen consoles on 2004/2005 era hardware (like the consoles) by reducing graphics settings.
And convenience (loading between zones) can be masked with semi-interactive loading areas (like Gears of War 4 which has zone loading but it's handled seamlessly with enemy free travel loading zones where you still control your character) or advanced streaming technology. Not a solution for all games, however, as some games want to have dramatic differences between areas (levels) of the game.
Again, however, I can't think of a single multiplatform game that doesn't run on 2009/2010 era hardware. It may not run well as no effort was put into scaling graphics beyond the minimum supported hardware configuration, but sometimes it does. Even AC: Unity will run, albeit not well. But AC: Syndicate using the same engine will run much better on that older hardware.
In fact thinking about in terms of launch titles. We saw many examples of developers over-estimating the capabilities of the current generation of consoles and then having to scale things back graphically or live with uneven or poor performance if they refused to scale things back too far. IMO, that would situation could have been avoided had there been a 2009/2010 consoles to provide a more gradual increase 3/4 year hardware iteration (the 6-8 year dramatic differences would still exist).
And while no examples can be provided for 1st party exclusive releases, I'm not seeing anything there that wouldn't run on a hypothetical 2009/2010 console by scaling the graphics down. Uncharted 4 is just a more graphically impressive Uncharted. HZD is just an extremely well executed UBIsoft formula open world game and the lowest console hardware it'd have to support would be the PS4, anyway. KZ: SF doesn't do anything noteworthy other than graphics. Same applies for the XBO exclusives.
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Whoops, I forgot to address
I've not been shown this. How are you even measuring this? And how is the console landscape more fractured than the PC landscape? And why is it even relevant to what consoles are doing? You cant upgrade a console other than boosting storage. If you want better performance you have to buy a new console.
I showed this with a brief example of some lines of core gamer oriented graphics products (for example, 480-580-680-980-1080), and how they have a far higher upgrade rate than do non core gamer oriented graphics products (for example 450-550-650-750-950-1050 which are targeted towards more casual or budget oriented gamers). The lower you go down the scale the higher the percentage of users holding onto their hardware, much like we still have X360/PS3 owners who still haven't upgraded.
Regards,
SB