I tried the 3.19.0-031900rc5-generic mainline kernel on that installation and both mutter and compiz based DE's work OK with nouveau, but the nvidia module fails to build properly against that kernel. I haven't yet researched what kernel we intend to ship with Vivid.
I started some testing with Ubuntu GNOME 20150125 but it's been bumped to 20150126 now so I'll wait until I've repeated those tests with the latest build before commenting further.
I tried the 3.19.0- 031900rc5- generic mainline kernel on that installation and both mutter and compiz based DE's work OK with nouveau, but the nvidia module fails to build properly against that kernel. I haven't yet researched what kernel we intend to ship with Vivid.
I started some testing with Ubuntu GNOME 20150125 but it's been bumped to 20150126 now so I'll wait until I've repeated those tests with the latest build before commenting further.