The point is that most people here don't care about native 4k yet because most people even on GAF don't even have a 4k TV at this point, so everyone is just basically saying: "Hey MS, just make the games look the best they can without just upping the resolution!"... and that's a sensible response. The current generation of consoles wasn't yet powerful enough to easily render all games at full 1080p/60fps, so while now dialing up to render 4x the pixels will make games look a lot sharper, there's a lot more you can do to make a game look BETTER other than just upping the resolution. We'll see tons of examples where a 1080p game will just look objectively better than a lot of the 4k games, simply cause it's not just all about resolution.
What people have to remember though is that TV prices are rapidly falling and Scorpio will only be released in a little more than a year. By then, you'll get good 4k TVs for 1k USD or less and by then a LOT more people will have upgraded, so Microsoft is just preparing for that case. And they're leaving it up to the (third party) developers how they'll want to use the power anyway. I don't think it's super smart to say that 'all First Party Games will render at 4k', since that's just an arbitrary statement to make. If 343 figures out some new tricks to make the next Halo look absolutely stunning, but can only manage to do that at 1080p, why would they make the game look less stunning just to support 4k?
I personally wouldn't expect 4k games on Scorpio to look DRAMATICALLY better than current gen games, simply because rendering at native 4k comes at a HUGE cost and that cost could otherwise be used to make 1080p games look insanely good.