When will custom numbers be able to be left "off" in the new layout?  That is the key.  You are forcing people into the new layout, but the new layout is not allowing custom numbers to be turned off, which is going to break a lot of integrations, including ours.  You should not be able to just "break" our business at a whim.  Don't force the new layout until the new layout can accept custom number setting as "off".  Period.