The Optical drive inside the PS4 is a BD-XL optical drive, the playback of UHD disc's were not included to mostly save on costs for playback licences.. The optical drive is mainly for BD-Data read only for games.. The Standard BD movie playback is rightly So cheaper, and since the HDMi port controller chip is HDMi 2.0a compliance along with a Upscaler it's a cheaper solution to provide 4K movie playback. The BD-UHD optical drives are more expensive because of the licence's to decode, the increase cost in HDCP licence's, and top it off its pretty early still for wide adoption.

I see. I find it a shame because it really could have been the ultimate 4k/2160P box(gaming, streaming, UHD blu ray, HDR) that would compliment essentially every 4K TV available. It still can, although serious videophiles like myself can't help but feel it is a serious omission. I feel Sony could have captured most of the 4k market but who really knows. Maybe the cost increase of a UHD blu ray player would have turned off more purchasers than it would have gained videophiles...

Rumors have it , that just to increase the PS4 optical drive to playback cost per dive would have increased to an additional $15.00 to $28.00 per drive!

Microsoft really surprised everyone out the gate with UHD blu ray implementation in the Xbox One S!

Well if you think about it, the original Xbox one HDMi chip was not a dedicated HDMi controller at all it was grouped and included into the South bridge ..but the S on the other hand has a dedicated hardware HDMi controller, and its a real good one , like the PS4's HDMI controller chip.

Here is the Xbox one S's HDMI controller

http://www.ti.com/product/SN75DP159

I can't find much about the actual drive, yet this is what DF said in the beginning and has repeated at every revision that there haven been no changes to the blu-ray drive

http://www.eurogamer.net/articles/df-hardware-spec-analysis-playstation-4

The Blu-ray reader gets a decent enough upgrade from PS3's 2x drive, moving up to a 6x CAV (constant angular velocity) design, meaning maximum read speeds of around 27MB/s - though throughput will lower according to the area of the disc being read. The spec appears to be a very close match for the standard BD drives Sony itself currently produces, lending further evidence to the notion that we're looking at a cost-effective 50GB dual-layer unit rather than the more exotic 100GB quad-layer drives said to be coming in the future to accommodate 4K video playback.

Yet you think it's just the license that makes it's almost twice as expensive? If it were as simple as a software upgrade, they could sell 4k UHD playback software through the psn store. You have to download an app too for the XBox One S, which is likely to save on license costs as MS only has to pay those for the numer of app downloads. The same way you had to activate certain codecs online on the ps3 last gen.

Yet maybe I'm wrong. blu-ray license apparently was $9.50 per reader in 2009. Maybe Sony had even planned to sell a software upgrade for money and were surprised by MS giving it away for free. Perhaps in Japan nobody cares about 4K UHD as 8K broadcasts already started last month...

Yet how can a BD-ROM drive read 33GB layer disks at 128mbps with a firmware update?

Eurogamer also noted that the slim and pro drive are still pretty loud. Further evidence that the drive is just a cheap component to install software from. Also from the XBox One S analysis "That said, one thing we did notice is that playback of UHD Blu-rays appears to be ever-so-slightly louder than standard BDs - and we wonder whether the disc needs to spin faster to read in higher bitrate video, resulting in more noise." (yet quieter than ps4 overall)
Seems to need to spin faster for 4K UHD.

In the end, if it can do it, why hold it back. It's not going to compete with high end standalone players and selling the license for $15 in the psn store is till better than not at all.

Yet how can a BD-ROM drive read 33GB layer disks at 128mbps with a firmware update? 

I can actually answer this one. Most ODDs are built to to have a large range of read and writes speeds so that they can use a single manufactured model for many different SKU's. The SKU's are differentiated by which Firmware version they have installed.

I have updates several drives' firmware in my way that upgraded the speeds of the drives. This practice was especially popular during the drive speed wars of early CD and Early DVD burning.  It just took a little bit of research and you could easily save $20 dollars by buying the lower end SKU and then firmware update it. 

This may or may not be possible with the drive in the PS4 Pro but this is very difficult to find out until after it is shipped.

Source, please...

BD-XL XD30-AGP1 the optical drive is a BDP-020 , BDP-025, BDP-010 reference Optical drive's KEM lasers. KES chipsets. Hell

Search this under Google:

BD-XL XD30-AGP1

Look at first results..grin

Take a look at a 6x BDXL pioneer drive

https://www.amazon.com/gp/aw/d/B00TL4HGB2/ref=pd_aw_sim_23_2?ie=UTF8&psc=1&refRID=0H713XSMW17MVEMWDGGX

https://www.blu-raydisc.info/licensee-list/flla-rom4player-licenseelist.php

Under ROM4..there is infact BDXL !

FLLA ROM4 Licensee List

BD-ROM4 Movie Player/BD-ROM Game Console/BD-ROM Test Player

NameCountry

Perhaps Sony are waiting it out, yet they didn't waste a lot of time enabling 3D blu-ray playback on the ps3. If they could, what's stopping them from enabling 4K UHD playback on all ps4 like HDR.