It is. I don't know what you're talking about. You can go ahead and apt-get xfce on Linux Mint right now. Back in 1998, I had Window Maker, Gnome and some other windows 95 inspired DE all installed in my Conectiva Linux. It was always possible.
I frequently do this to try out different DEs. My only issue with it is that if the DE has its own version of some package like a music player I end up with a cluttered menu with all version from all installed DEs. Would be nice if there were an easy way to limit each DE to its app list by default.
By default is a tall order. Most people want to have full access to their software library. But a GUI tool to edit the menu for a specific DE for a specific user...that would be nice.
Installing KDE Plasma on a Gnome installation breaks so much shit it's not funny, but most of this seems to be a problem with the command line because doing it with YAST seems to prevent things from breaking.
I don't get this. It is a common statement on lemmy especially among the new users. I have been daily-driving linux for many many years, and every install of a new distro gets 3 or 4 DEs added to play around with and find the 'flavour of the year' for myself.
I don't recall this ever being a real problem. Ever.
Been using Linux for 25 years, and I remember some of this from init script years, but it's been a long, long time since it's been an issue in any half-way decent distro.
I started with Conectiva in the nineties. Back on Gnome 1, fvwm, etc. Never experienced that. The opposite, it was always possible to run programs from one toolkit in another. The only issue was the aesthetic clash.
Manjaro does this with word processing software but I wish it did it with more stuff. It would be nice to not have to uninstall a bunch of apps and install my preferred ones as the first step after a fresh install
I've done this with debian in the past, you just install different DE in parallel. Works well enough, don't remember it causing any issues. It just makes a mess of your home folder, so I don't do it outside of testing purposes.