Ben Heck has now released a PS4 Pro teardown.
Ben Heck's PS4 Pro Teardown
The only really interesting thing there for me is that the PS4 Pro uses an identical blu-ray drive to the
slim version of the PS4, which to me at least, would probably account for the lack of 4K blu-ray support. They simply wouldn't want the additional expenditure of having to purchase two separate drives for the two consoles that they'll continue to sell. The two blu-ray drives even have identical enclosures so it is essentially a single unit which could save them millions in having to set up two separate production runs for the drive bay in both console.
It's a little different with Microsoft as they currently only have a single console to produce as the older version is no longer in production. I wouldn't be
too surprised to see them doing what Sony is doing and sharing as many parts between the two consoles to reduce the costs to them as much as they can.
Of course, there would have also been the option for Sony to have identical 4K blu-ray drives in the two devices to save costs but I do wonder if what they're using now is the same one they were using in earlier builds of the PS4?