Since the news about Cemu going open-source and available for Linux went viral a few weeks ago, we’re already starting to see improvements to the Wii U emulator with version 2.0-1.
To start, the update is mostly bug fix-related. Many of the issues present with 2.0 should no longer be a problem with this update. The patch notes also mention “lots of smaller Linux improvements,” although it doesn’t go into detail concerning what exactly has been improved. I suppose you could check the commit history if you want all the details. The developers mention that “we are still working on additional distribution formats (AppImage/Flatpak).”
Apparently a recent Wii U firmware update has screwed things around for people with North American Nintendo accounts who wanted to play online. That problem is now fixed.