As of today, Kubuntu is shipping with Cantata and VLC as Music and Video players. Both have their own UI which is not related to KDE at all. We should have modern-looking/KDE Designed basic system applications. Applications that are basic and should have the same design language:

* App/Software Repository Manager (ie Muon)
* Music Player
* Video Player
* Calendar App
* Text Editor (Kate is fine)
* System Settings

I know that Kubuntu "is not" KDE, but i'm pretty sure that if KDE had consistent applications shipped by default, Kubuntu would use them. So the question is, is KDE working into this, is there any roadmap? we are heading towards 2018 and we're lacking some basic stuff, very concerning to be honest.

VLC looks like a kde app to me. I'm using Breeze Dark for my main Look and Feel package, plus GTK 2 and 3. You can change the look of many non kde programs by setting a GTK theme under System Settings > Application Style > GNOME Application Style (GTK)

Some other programs have their own themes ie web browser. (I'm using Dark Moon theme for palemoon browser - (a firefox fork) - matches breeze dark really well)

According to kubuntu's feature tour https://kubuntu.org/feature-tour/
Dragon(video) and Amarok(music) come standard and both are kde apps https://www.kde.org/applications/multimedia/

VLC just happens to be cross platform and super popular which is why, I suppose, they include it.

VLC and Cantata are built on Qt, not KDE framework libraries. As Breeze includes a Qt style, they will use it and look visually integrated with the rest of the environment (which is perfectly acceptable). It just means that they may have had to reimplement or go without features provided by KDE framework libraries.

There was some work on a new KDE-based music player called Elisa which was discussed a bit in the VDG forum: viewtopic.php?f=285&t=137709. Looks like that at least made it into the extragear repo, so should be easy enough for distros to bundle and include in their repos (once it's stable enough). There was also mention of another media player designed by Andrew Lake of the VDG; but I don't know if that made it past the mockups that he mentioned in that forum topic.

As for video, I believe Bangarang, which was also designed by VDG members, is intended to fill that space (probably both music and video).

Of course I don't see a problem with just going with VLC for most Video media since it's arguably the best Video player around.