I’m running Mint 18.3 on my laptop (as I write this) and on my home desktop system. I’ve always used the KDE versions of Mint... When it says “no KDE version of 19.0...” does that mean no KDE spin of it *yet* or that they are no-longer going to provide a KDE version of the distro? :-(
Mint is pulling their support of KDE.. so.. if you still want to use KDE, then you will have to manually install KDE after the initial install (18.3 is that last version of Mint KDE, but it will still be supported until 2021).
My understanding is that they will no longer have a KDE spin of Mint. If I am wrong, someone will correct me.