Aside from being based on Fedora 39 now, KDE is now the official desktop environment replacing GNOME. The reasons why are in the article.
The GNOME version of Nobara still exists, but it’s going to be the vanilla version shipped without any extensions (probably because many of them broke after moving to Fedora 39)
Even before the switch of the default was Plasma already an option. It just wasn’t the default.
Fair enough. I find if it’s the default option, it’s a better out-of-the-box experience as the devs would have spent more time on polishing etc.