The more that I think about this, the more excited I get about it and want it to be true. I'm totally fine with this as long as there aren't any ps4k specific game releases and it's regular ps4 discs and digital releases that are run on it.
As for the some devs are happy about it, and then that subsequent post for a dev saying he (or she) wouldn't be.I can see how that could be the case (some being happy about it). It is entirely optional to a dev if they want to create and include some sort of setting template for the ps4k on the disc or through a patch that enhances performance/fidelity.
Some devs may forgo adding in enhancements whatsover, which would be a bit disappointing, but understandable, especially if it's a smaller dev.
Some devs may do a bare minimum type deal where they let the hardware to the heavy lifting rather than optimize every little thing. Like say the ps4 version is running at an unlocked framerate (with a 60fps cap), just leaving the game that way would the ps4k brute force its way to 60fps, and it will do that with ease if the game runs above 30fps on the ps4 as it is. Others may implement some better form of AA. Others may simply improve the resolution.
And some devs may go the extra mile and properly optimize for the system, and it may feel like a worthwhile proposition to them if they have a marketing deal going on with Sony, as they can then use this better looking/performing version of the game to market/demonstrate it.
And of course there are some who just like having some more power to work with while making a game.
(But yes, this doesn't mean that I think that all devs would be happy or indifferent about this.)