I love this discussion, I feel like I know where people are coming from as doubters and where they're coming from as assured that the downsample (supersample) from checkerboard 4K works, now, too.
I think there's still room for doubt, and despite me now moving to feeling a little more assured that it's just going to supersample on 1080p whether or not the developer intends that or not, truth is, Sony hasn't actually specified in an official way to know for sure yet.
Given the impressions of the TGS build running on PS4 Pro, it is absolutely a strong desire for me as FFXV will be one of my first post-Pro titles, and also happens to be one of my most anticipated titles as well.
I understand for sure that Sony has communicated that checkerboarding their games up to 4K on the Pro is relatively simple because it uses a customized, hardware built-in function from their APU (GPU) that costs the developer very little (if anything) in terms of performance, so the expectation is that developers will, of course, take advantage of using it as part of the Pro feature sets. One place where I'm getting hung up though, is that I don't think Sony has completely confirmed that the checkerboard technique also automatically supersamples back to 1080p from a hardware standpoint. That is, in order for it to achieve that supersample back to 1080p, the doubt here is whether or not developers have to enable this to happen themselves -- the PS4's custom checkerboard hardware does not necessarily have the function of handling the supersample function on 1080p displays, instead perhaps requiring devs to have coded their game to re-purpose the 4K checkerboarded image back to a 1080p output manually. Again, as my last post said, that particular Cerny quote from Engadget interview has me feeling more sure that the supersample function is built into the hardware now, though I admit some doubt is starting to return.
I get that Sony has the 1080p native render+base framerate parity mandate in place for all PS4 titles going forward post-Pro launch, and that for some titles that render below 1080p on a base PS4, this will still be an IQ improvement.
It also does pose the question of what the data transfer bandwidth requirements are for the checkerboard technique. If it's handled automatically on the hardware side, I think the supersample back to 1080p might just make it a very slightly higher bandwidth requirement than a normal 1080p signal, but those looking to output to 4K (and with HDR) displays will have to meet the HDMI 2.0 standard. I'm not sure if supersampling back to 1080p means the cable and the display interpret the signal more like a lower-bandwidth 1080p signal (seems more likely to me, if it's handled automatically by the hardware) or as a high-bandwidth 4K signal. I'm just not well-versed enough in the technical aspect of digital a/v signals to have an educated idea of this particular area of concern.
After participating in this thread, I'm currently feeling like Sony's going to deliver the best scenario here, with the built-in checkerboard hardware probably handling the supersampling feature itself and not requiring additional developer input.
Clearly, however, Sony has kind of failed to communicate this clearly.