How would you like to be able to use Universal Transverse Mercator coordinate system with the Maps extension? Do you want it in inputs and/or in outputs?
Do you want only "standard" UTM or also variations like MGRS (Military Grid Reference System), MTM, SCOPQ (Canada) or Gauß-Krüger (Germany)? Or even Transverse Mercator coordinate systems based on other map data such as OSGB36 and Irish Transverse Mercator?
I believe that the Universal Transverse Mercator coordinate system is not supported by the Maps extension. Is this something that could be implemented eventually?