What I meant was that if he wants to try out Gnome, he should install only few extensions to have a vanilla experience. Then he can install the extensions he wants. I would have said the same thing for KDE or any DE.
“Try first without tweak and when it’s work and you like it, try modify” something like this.
I don’t really use KDE, and if I forgot some really crucial information thanks to correct me.
You can use the KDE spin version of Fedora with plasma 6, or if you love the rolling release of Arch you can try openSUSE Tumbleweed with KDE (you choose you desktop environment at installation).
And for what you going to loose if you go to GNOME :