GNOME Bugzilla – Bug 667466
Add GtkSourceBuffer support to Glade file
Last modified: 2017-03-03 13:36:21 UTC
Looking at data/glade/gtksourceview.xml it seems to support the GtkSourceView. However it does not contain an entry for GtkSourceBuffer. Or any other Gtk widgits that may exist, though it looks like that is the only one.
Unlikely to happen.