I'm interested to learn why they chose to switch to Gnome instead of KDE plasma. What was the thinking behind it? Why wasn't the community involved in the decision? Gnome has the backing of Redhat and is the default DE on Fedora, so Canonical backing an alternative would have been desirable.

I'm biased, but Plasma or even Mate would have been much better choices. Plasma has been so good lately and seems to take community feedback seriously. Stability has been great, it's extremely lightweight and the customization options make me...happy. I've been kicking myself for not switching from Gnome to plasma sooner. For anyone skeptical of plasma, I urge you to give it a try : kubuntu, kde neon, fedora kde, arch + plasma, opensuse are all great.