I'd say that depends entirely on whether glade3 can handle all glade files produced by glade2. Can it ?
http://glade.gnome.org/ says: "...respects the same XML format as glade-2" However, I am yet to verify the truthfulness of this claim. I plan to look into it once I am finished with Anjuta.
In case they are incompatible and we decide to continue with Glade2, then we might need to drop Anjuta, since Anjuta will most likely have Glade3 as a dependency. Or would we then want to split Anjuta into -plugins or -glade3?
Cheers, Debarshi