Not necessarily a major delay.
PES 2017 was set to get an update enabling PS4 Pro support at the end of November- however, it doesn’t seem like the developers at Konami will be able to hit that date. In a new statement released today, Konami confirmed that the PS4 Pro patch for the game had been pushed into mid-December, apologizing for the delay.
The PS4 Pro support is actually planned to be fairly minimal, if reports are correct. It is clear that the game will get a 4K resolution mode, but that seems to be the only visual or performance based enhancement that we know of. In fact, whether or not that 4K resolution will be achieved natively is also something that we are unclear on for now.
The PS4 Pro launches today worldwide, for $399. PES 2017 launched a couple of months ago, and is available on Xbox 360, Xbox One, PS3, PS4, and on PC via Steam.