Let me introduce myself first. I am a member of KDE Promo group and the guy behind Plasma release videos. I was also involved in making Kubuntu 15.10 release video.
Given the recent changes in the Ubuntu I think that Kubuntu have a great opportunity to become more visible. One of the ways to do this is by shipping high quality applications. This task is only meant to spark a discussion.
Amarok - no longer maintained, no port to kf5. -- //REMOVED//
Cantata: https://github.com/CDrummond/cantata -- ON BETA ISO
KDE telepathy - unmaintained -- //REMOVED//
As a matter of fact it seems that Empathy and telepathy are in similar situation.
Telepathy doesn't work with most most popular chat protocols which are mostly closed nowadays.
The only alternative I can think of is Telegram which is quite popular among KDE users (open source client, closed server side)
Torrent client -- KTorrent KF5 installed
Video player -- VLC Installed
VLC - http://www.videolan.org/
KDE PIM or to be more precise KMail is perceived by some of our users as too complicated. Given the fact that more and more users are using web clients shipping KDE PIM by default is questionable. Alternatively Trojita http://trojita.flaska.net/download.html may be a better choice.
Of course this is very subjective opinion.
I know that some of these applications aren't strictly under KDE umbrella, however we should be pragmatic and choose the best application in each category, as long as they integrate with Plasma desktop.
As I said earlier this task is only meant to spark a discussion so any comment/opinions welcome.