The difference is that one of those sets of standards is actually more of a file system hierarchy and API standardization thing, whereas the uni-desktop would presumably force a particular set of gui widgets along with the filesystem hierarchy and APIs that those widgets are built on.
We of course already have something like this (POSIX, Freedesktop, etc). However neither is abided by very well and neither of them go far enough up the stack to deal with certain very visible issues of desktop application incompatibility.
What I think could be done to fix some of the compatibility issues (like when running QT on gnome or GTK on KDE or applications that eschew them both and have janky window decorations) would be some more serious standardization onto something like Wayland. We would of course need something more than a reference implementation for that, but fundamentally I don't see why that would be too restrictive for projects that still want to make their own widgets.
We of course already have something like this (POSIX, Freedesktop, etc). However neither is abided by very well and neither of them go far enough up the stack to deal with certain very visible issues of desktop application incompatibility.
What I think could be done to fix some of the compatibility issues (like when running QT on gnome or GTK on KDE or applications that eschew them both and have janky window decorations) would be some more serious standardization onto something like Wayland. We would of course need something more than a reference implementation for that, but fundamentally I don't see why that would be too restrictive for projects that still want to make their own widgets.