I bought a PS3 years ago, mainly for the blue ray player and for the streaming support (stream from a NAS upstairs to the DLNA media server on the PS3 downstairs)
It is expensive to buy just for the blue ray player, however one thing it did notice and was quite happy with, was the PS3 did always have the latest support via software upgrades for the latest blu ray player changes. Some stand alone players firmware can be updated, some cant, some only to certain levels - like when the 3d support came out, the PS3 got an update and it then supported that, i noticed at the time a lot of stand alone players couldnt be updated - meaning having to rebuy another one. I was never interested in the 3d bit anyhow, but was quite impressed that the PS3 always had the latest development support for whatever new features that the blue ray people decided to release.
Anyhow ended up getting a media server WD LiveTV box to handle the streaming part as i stopped buying blu rays and had most of the films i wanted in file format, gave the PS3 to my brother so his kids to use it for movies/games.
New 4k blu rays are starting to be released, and obviously that means an update to firmware to support this. I would imagine the PS4 will continue to get updated to handle this.
Depends on what you need. If you dont have a collection of blu ray discs already and are thinking of getting them and a player, i would say that maybe PS4, although expensive, will probably allways have the latest support. Some stand alone players might also, might have to check manufactures websites/forums to see what other users are saying/asking.
I havnt bought a dvd or blu ray in over 3 years now, most of the stuff is streaming/downloadable - hence me having a NAS box to store files and media server for downstairs. Also now that i think of it, 2x bricks and mortar retails stores closed in the town where i live that did sell dvds/blu ray discs, the last one closed last week, and a third (the last in the town) is due to close a chain of stores in next couple of months (they rent dvd/blu ray and sell them). So the reality is that in my town at least very soon there will be nowhere to purchase a dvd/blu ray, if i so desired to do so. Looks like the future will be online content.
Hopefully that gives you some info to help you make your decision.