I am eagerly awaiting the first release of Devuan!

Alien BOB, aka Eric Hameleers has done a very good job of building KDE 5.2 for Slackware without systemd, although it does have wayland
While it hasn't been "officially" released for Slackware it is looking really good so far. It does have a few bugs in it but that should be considered normal for what he has to go through to get it to work.

When the time is right, maybe he would be able to help or just be able to give some pointers.

http://alien.slackbook.org/blog/kde-5-plasma-5-2-0-available-for-slackware-current/