You guys do know that console games in development actually can have graphics settings (in a menu taken from the PC version or in a debug menu) that you can change, right?
Developer effort will come more in the sense that they have to keep the different performance budgets in mind. Meaning, if you need to keep, let's say, your polygon budget under 30M for the PS4/Xbone version you make a graphics setting around that, then PS4k would have an undefined number. You would then add props, details, change LoD to use that extra PS4k power.
It's no different from doing different graphics settings for PC.
They'll probably make a baseline in the future, like PS4 = Low/Medium = 7850/760, PS4k = high/very high = (future) Polaris 10/480, and that's the way they'll manage the difference in power.
It's not very different from what happens now with multiplatform games. Extra platforms always mean extra hours in compliance, QA and builds though. But games won't be (or shouldn't be) any worse for it.
Source: the brain of an actual person working at an actual big studio
PS: I'm guessing a lot of the time they'll just throw some HBAO, higher quality filtering, they'll move the framerate lock to 60/increase res and maybe add some AA.
