Will be very good idea because : kde needs at least 768 mb ram and 1 Ghz cpu and xfce4 need 300 Mhz cpu and 400 Mb ram ! So at default (kde) whonix need 2 Ghz cpu and 1536 Mb ram {ok,its virtualized but the diferances in performance is very notable still} and xfce4 whonix need 600 Mhz cpu and 800 Mb ram ONLY ! The xfce4 desktop have evrything , that can do kde can do and the xfce4 , ok kde have better graphics but xfce4 have allmost the 1/2 minimum system requirements and for that runs much faster and in older machines!
As for the most importance of all , the security risk , yes that is the reason even i i dont use xfce inside whonix , The reason is the test , must someone check\test the xfce for security , probably xfce is as secure as kde , i all ready test xfce4 in whonix for performance and apps, it is awsome!
Good day,
we have had the suggestion of using more lightweight desktop environments come up multiple times already and at the moment, it would be far harder then it may seem to maintain multiple DEs at the same time. Security issues, compatibility, usability, all these things would have to be considered. Adding to that, bringing out additional images for VBox and KVM would eat up a lot of time. At the moment KDE is chosen mainly out of a personal preference by the developer, as stated here: Frequently Asked Questions - Whonix ™ FAQ
You are of course encouraged to change the DE as long as you are aware of the possible complications and issues this may bring with it.
Have a nice day,
Ego
understood , thank you.