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.
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).
