Let me start off by saying that I'm aware the new KDE5/Qt5 integration is due Q1 2019,
and I was simply hoping we could get this flag enabled in the meantime since I don't
see any harm in doing so presently. (To my knowledge you'd have to export
SAL_USE_VCLPLUGIN=gtk3-kde5 in order to use it)
I'm behind rdieter's wish to gut the remaining KDE4 support, and also behind
Kevin's idea that doing so should wait until Qt5 support comes soon.
Regardless, people should have the option to use gtk3-kde5, since it's a new feature
in 6.1, and I don't think it's mutually exclusive to the task of removing KDE4
I think KDE4 support is a big enough umbrella that it warrants its own ticket - that can
perhaps also serve to track the impending KDE5/Qt5 support as well.
- Michael Goodwin