If you have troubles with playing files via DLNA, you might want to check if the server profile is for PS4. At least with Serviio, if I leave it on the PS3 profile it would ignore all the mkvs etc. because it knows a PS3 can't play them (or it will use transcoding if you have that active).
The other thing is that people often don't know that mkv, mp4 etc are just container formats. It still depends which codecs are actually used and if the PS4 supports them (e.g. H.265 doesn't seem to work yet = that mkv won't work).
There are only very, VERY few odd files that don't play in my setup. That was way worse on PS3 even when the codecs should work on paper.
Update is kinda meh feature-wise, the player itself is still very barebones compared to the PS3 one. Mainly, I want the volume option.
I don't think much changed for subtitles, I already had them working in mkv and mp4 before (again, check your server settings to enable embed subtitles via DLNA, then adjust the PS4 settings). It seems the only difference is that the PS4 now auto-directs you to the actual system settings for closed captions. Before, you needed to know that those exist or the subtitle toggle in the player wouldn't do anything of course.
I have some odd files in which subtitles didn't work (probably only certain formats are supported by the PS4) before the update and they still don't, so...
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HOWEVER, the megaton for me is that this update fixed the bug that would lead to movies with certain codec/container combinations getting massively out of sync near the end. That was very frustrating as the files would run fine on PS3.