Thread:Extension talk:Maps/Adding custom maptype/reply

Maps used to allow defining your own layers for the OpenLayers service. This functionality is currently broken and hopefully will be added in back in the next release. It never had support for doing this with Google Maps though. Perhaps the person working on this functionality has taken care of this now as well though, I'm not sure - will ask.

Either way, feel free to create a feature request on bugzilla.