Making windows slightly translucent when moving has always seemed gimmicky and purposeless to me. KDE Neon ships with the feature off, but Kubuntu doesn't. I think it would improve the user experience to ship with it turned off.
FWIW: I use the feature quite often when positioning windows over each other to make sure relevant information is not hidden when another window pops to the front. As the feature does not hurt when on: -1 for removing it.
It's there for me in Neon on my hardware. It's not a case that Neon does not install it, as it's all the same Kwin lib. Simply that Kwin only displays it as an option if it determines that your system supports that for the compositor.
Also -1 from me for setting any config in kwinrc etc to disable it by default.
Ah, makes sense.
I stand by my position that it's a bit of a cheap, amateurish effect in 2017 for a mature and professional desktop like Plasma, but if that's just me, I'll go back to my hole and shake my cane at clouds again.