From reading this:
https://www.ghacks.net/2017/10/27/linux-mint-kde-is-out-lmde-3-is-in/
It just looks like the mint devs are dropping the KDE flavour, because they themselves are more focused on GTK/Gnome based development, rather than QT.
But I'm sure that all of the QT/KDE applications will still be available in the repositories.
The KDE desktop may also be available in the Mint repositories - it just won't be available as a default desktop in any of their official versions.
So the mint devs are only dropping their official KDE re-spin of Mint - with KDE pre-installed.
The KDE project itself seems to be thriving still.
I'm not sure why Jovie got dropped.
All I can find out at the moment is that it never got ported from QT4 to QT5.
I didn't bookmark the site, but I read something last night about a Speech library that is built-in to QT5 - so perhaps that is why Jovie has been dropped.
KDE projects are all based on QT, so if QT has a library which natively supports TTS, then I suppose it makes sense to drop Jovie and use the QT TTS module instead.
Here's the home-page for the QT TTS module:
https://wiki.qt.io/QtSpeech
Looks like it's still a WIP.
I read a claim elsewhere that it is possible to manually re-compile Okular from source and enable TTS via the new QT5 TTS library by enabling the TTS option in the config before building.
But that article also claimed that adding TTS currently causes some instability in Okular, which is why most Linux distros are shipping their pre-built versions of Okular with TTS disabled.
So perhaps we will see the TTS support restored to Okular when/if it becomes more stable. IDK!