gnome-extra/gnome-do-plugins ebuild declares dependency on dev-util/monodevelop, which seems to be redundant. I have dev-lang/mono, but not dev-util/monodevelop, and I could successfully emerge gnome-do-plugins suppressing monodevelop installation with --nodep. Build succeeded, and plugins were installed and working. It seems that dev-util/monodevelop dependency can (and should) be replaced with just dev-lang/mono.
Previous versions used mdtool as part of the build process and this tool is distributed as part of monodevelop. But as you already checked gnome-do-plugins-0.8.2 no longer has this requirement and builds fine without mdtool present. I've removed the monodevelop dependency, thanks for the report.