-Targeting two very similar (architecturally) hardware specs isn't going to be an issue for developers. It still pales in comparison to, for example, making a PC game.
-Speaking of PC gaming, a shorter console cycle benefits it greatly. The drawn out 360/PS3 cycle was terrible for PC gaming.
-It's not like any smart developer is actually going to target 4K native if they're trying to make the best looking game possible. Serious diminishing returns. 1440-1700p upscaled is good enough, and then you can put the additional graphical power to use elsewhere where it will make more of an impact.
-From the sounds of it, this is totally happening, and has been corroborated with multiple developers. Honestly, Sony and MS would be insane not to chart this course since either one would be screwed if the other came out with an updated console but they didn't.