I've not seen it, but keep getting promised its coming. Its not just an MG issue, ALL new Meraki products MG, MV, MT fail to work with existing templates. The answer, just break your existing production combined networks with Appliances, Switches and Access points, create a new empty network of type M(x) and recombine. Problem is if you pull them from the templates and put them back in you run the risk of losing modified settings / ports or IP ranges on the MX's on production networks!!
Anyone on here from the MG product group (or MV, MT) have an update. I'd agree this is not resolved until we have a proven way to migrate existing templates without impact to operations. Should be as easy as "Add Device" regardless of age of template ......