Actual proper touch support, which includes a decent built-in keyboard (looking at you KDE...).
I love 2-in-1's, but I do wish touch support would go all the way. It's like... 70-80% there, with Gnome having a good keyboard and KDE having the better touch support overall. But it just needs to go the final stretch to make it a good experience.
Completely agree. Like you, I found Plasma to be a much better DE with a touchscreen than GNOME (ironic, isn't it?).
maliit-keyboard is not bad even now (responsive, fast and beautiful). But there are still problems with the fact that it does not work everywhere (some sites, Signal Flatpak).