I'm going to try to close this thread. The decision to not include UHD Blu Ray on PS4 Pro was solely for compatibility- with existing and future PS4 games/software. It wasn't to cut cost, that they didn't believe in the platform, etc. It was one less component to worry about when making sure all games worked across all systems. I know the argument can be made about just matching drive speeds, the games save to the hard drive, or that it shouldn't have an affect at all. But it is one less big component to worry about if a game/software did not play correctly. Does it suck, sure. It was, however, not a dumb choice on their end or an oversight. It's the same drive that is in the PS4. It also adds another key feature to promote future PS5 purchases.
Also the UHD format is not entirely set, in the way that Blu Ray saw a lot of changes in its early years, so much so they re-released newer versions of older Blu Ray titles. Think of the updates 300 saw with video and audio. Also to look out for future 4K TV purchases, it is still better to wait for all current standards to get out and settle. We can expect technologies like FreeSync to move into TV's which would make for a major improvement, HDMI 2.1 which will see big changes for HDR, also TV's with higher nits to display a broader range of colors. If requested I can explain why purchasing current OLED tv's is a bad move.
Can we move on.