I support moving away from KDE, and that’s coming from a long-time KDE fan.
There’s a couple of reasons for this:
- KDE includes a lot of overweight stuff that isn’t really relevant.
- I think the shell for XFCE makes a lot more sense in a VM. (launcher at bottom etc)
- I moved away from KDE some time ago and have been using i3wm for ages now on Qubes and have found it a lot more stable. I’m not suggesting to use i3wm in Whonix though you could easily install it if you wanted. Eyecandy is overrated and it gets old fast. Having something that works quick and with a lot of stability never gets old.
- I borrow a lot of things from XFCE like Thunar. I agree it’s certainly a more mature environment something which would benefit Whonix because that isn’t the distribution’s focus.
- The new version of XFCE (4.14) will have pretty much everything I want out of it, HiDPI GTK+ 3 etc.
- I suspect the surface area of XFCE might be considerbly less.
what do you think of the Enlightenment Desktop? It was designed from the ground up for devices with low computing power and can function with all KDE/GNOME software.
Enlightenment has a lot of very special stuff EFL, ESD etc. I don’t really think it’s that much better on memory either. Yes that’s from 2014 but I doubt it uses less now than it did back then. A more current benchtest. It’s actually really hard to find any tests for Enlightenment because it’s not very popular (ie very few distributions have media that includes it.)
You are going to have problems with it you won’t have with XFCE 
due to the specialized nature of it.
I think XFCE makes more sense as ‘complete package’. It also helps that it doesn’t have releases all the time either. I think XFCE is also a better option as it’s officially supported by Debian’s live-cd project whereas Enlightenment is not. I also don’t think Cinnamon is nearly stable enough having tried that.
As for KDE, well it may look great, but that comes at the cost of resources and disk space 2.2GB for GNOME 2.4GB for KDE and 1.8 for XFCE. Both of these things are at odds with the aim of Whonix.