The point though is that there used to be a «Linux desktop» you could target before the Wayland transition. Fragmentation of an already small market segment is unfortunate.

It's KDE now. GNOME is the penguin that went to the mountains while KDE largely tries to be compatible with things that aren't KDE.

Sure. I use KDE myself. I actually like the Gnome default UI/UX more, but I'm really not fond of their "our way or the highway" approach when it comes to customization and interoperability. KDE feels more in line with the true FOSS "spirit", and after a bit of customization, fits my needs better than Gnome.

There was not really for system utilities. Apps, sure, but not system utilities.

What do you refer to as system utilities? All the stuff now subsumed by SystemD?

Things like input methods, certain accessibility functions, screen savers and similar things.

Huh? Fcitx and IBus both worked on GNOME and KDE as far as I'm aware. Now, Fcitx using QT and IBus using GTK helps them feel more native on KDE and GNOME respectively, but they would both work.

Doesn't seem possible on Gnome and not very straightforward on other DEs according to the arch wiki: https://wiki.archlinux.org/title/Fcitx5#Integration

It seems to me that the issues on that page are Wayland-specific; anectotally, on my random X window manager works fine with Fcitx (except for Emacs, but that's probably Emacs' fault, not the IME protocol's).

No, that's a terrible idea. The right thing to do is design a Wayland protocol that gives you the access you need, get it accepted into wayland-protocols, and wait for all the compositors to implement it.

Yes, that's a slow, annoying process, but doing something bespoke means either you do the same work over and over for every compositor, or you only support one or two compositors. Neither of those is a good result.

It is way faster and better to implement what you want/need in the DE. Later, it it makes sense, you can standardize it.