I have hopped around distros a little, Manjaro (hated AUR), Fedora KDE Spin (not my cup of tea, it was fine but eh!), Kubuntu (this was my happiest place, but still wanted Mint), even Mint Cinnamon 19 (Hate hate hate cinnamon). I wanted Mint 19 and I wanted KDE, it's my happy place. As a Linux user since 1994 (OS/2 prior to that) I am no stranger to hacking things together, but am at a point where I want things to "just work" and none of the above has except for Mint KDE (I love KDE and have used it since 1999).

Another post here got me thinking and I tried it and I ran into a perl configuration issue during -dist-upgrade but that was an easy work around and now I am now running on Mint 19 KDE!

Below are the steps that I went through to make it work:

Pre-requisite is having a fully updated 18.3 KDE install on your system:

1: Open Konsole
2: Update Repositories: Change Xenial to Bionic and Sylvia to Tara
sudo vi /etc/apt/sources.list.d/official-package-repositories.list
sudo vi /etc/apt/sources.list.d/ubuntu-defaults.list

3: sudo apt-get update
4: sudo apt-get install apt go url
5: sudo apt-get install mintupdate libgtk-3-0 libgtk-3-bin

6: Log out then log in again.

7: Open Konsole:

8: sudo apt-get dist-upgrade

If/when dist-upgrade fails:

9: sudo dpkg --configure -a
10: sudo apt-get update
11: sudo apt-get upgrade
12: sudo apt-get dist-upgrade
13: sudo apt-get install -f

14: reboot

You will lose the Mint background, but other than that you will now be running Linux Mint 19 with a completely updated KDE from the Kubuntu backport repositories.

You should have a look at Neon: neon.kde.org