That image isn't an "official" Trisquel install, it's Triskel, which is a
KDE-based derivative of Trisquel. I wouldn't expect it to be representative
of what Trisquel 5.5 will actually look like. To my knowledge it hasn't been
decided to move to XFCE yet (from Quidam's post here
http://listas.trisquel.info/pipermail/trisquel-devel/2012-January/000556.html
although someone who hangs out in IRC might know about more recent
developments)
Gnome Shell, Gnome fallback mode and Unity are pretty much ruled out.
Consensus on the thread seems to indicate that Mate is too unreliable at this
point. XFCE looks like it could be a good choice, actually. I've never
actually used it but it looks like it's compatible with Gnome Panel applets,
so you could build a Gnome 2-ish experience with it. Honestly I'd love it if
Mate were the default desktop for 5.5, but I doubt that would be the case.
Or maybe I'm wrong and Trisquel will actually be KDE-based from now on.
Personally I hope not.
