The matter of PCManFM-Qt, I mentioned that here in May (only one, who responded btw). Keeping half the app window to look at the folder/partition names is a waste of area. Dragging is not the solution.
Plasma-desktop is available in the repos. Anyway, there are so much KDE packages in Lubuntu-qt.
It was not my original idea to install Plasma DE, but it was just there.
Good, but it is not a problem to create that session. LXDE is something that cannot be deleted too from the repos for quite sometime. Openbox is not going away in the far future.
Well, that question cannot be avoided. The link to Lubuntu 18.04 release is deliberately hidden here, while Lubuntu 16.04.3 is there. I had to go “previous releases” to find that. So, when Lubuntu 18.04 is hidden away, with the old Lubuntu in it, why not change the name to Lubuntu-QT, or Lubuntu-LXQT? The Lubuntu was/is Openbox+LXDE and it is not going to be there.