That reminds me of the PS3 with the 3D blu rays.
At first it was not possible to read them and they were saying it's impossible without a 1.4 HDMI connection.
They after they sold their first super expensive Sony 3D blu ray players they came with en uptake to allow the PS3 to read 3D blu rays with its old blu ray player and its 1.3 HDMI connection.

You can't compare UHD Blu-Rays to HDR really. Original PS4's HDMI output supported HDR from the start but PS4's software didn't support it. For example, MS can't add HDR to original Xbox One because it has older HDMI standard which doesn't support HDR. The same thing with UHD Blu-Ray on PS4 Pro - the hardware (the drive itself) can't read UHD Blu-Ray discs, so this is not gonna happen via some software update

Errr..... thats not what happened.

3D blurays were part of the bluray specification. It was a feature built into tbe co fines of the specification. As long as a players firmware could support it then it would work as long as said player also adhered to the set specifications of the Blu-ray standard. 

the advantage the PS3 had over every other existing player at the time was that it had an update able firmware. I don't think it was ever a thing that the PS3 wouldn't handle 3D movies when sony also championed 3D games on the PS3.

I'm guessing this is all coming from a belief you have that Sony is somehow only doing this because they want to sell "super expensive" UHD players before patching the feature into the much cheaper PS4..... you are wrong. 

So "not absolutely impossible" means "probably" now?

I'll believe it when/if they do it. Such an omission is still completely mind-boggling to me.

everyone talked about it it when the XBox One S could do HDR and the PS4 couldnt, how it is the biggest deal in the world etc. better than 1080p native. Now everyone is quiet ounce HDR support came for free via an update for every PS4. On 10th november everyone can enjoy it for gaming.

the PS3 has an older drive and MS didnt patent the technology let alone they knowing how to do this like Sony

You should be careful with the word everyone because the way you are using it is the wrong way, generalizing a group of people that to you behave like a hive mind. 

We really need to assume worst-case scenario that the PlayStation 4 Pro would never play 4K Blu-rays. As long as Sony did not announce it, I would not assume it.

From PS4 Pro tear downs it can be seen that the Blu Ray chip is now located on the motherbaord instead of a seprate daughterboard installed on the Blu Ray Drive like it was on the original PS4s

http://www.psdevwiki.com/ps4/BDP-025

https://de.ifixit.com/Teardown/PlayStation+4+Pro+Teardown/72946

original PS4 daughterboard of the Blu Ray Drive having the Renesas SCEI R9J04G011FP1 processor

PS4 Pro motherboard having the Renesas SCEI R9J04G011FP1 processor on the motherboard (in green)

comunication, updating and flashing should now be a lot easier in order to run 4K Blurays on PS4 Pro