FWIW, if implemented, this probably ought to be a global setting under "Units of Measure" or "Map Settings". The reason I say that is that is when you tap on any spot on the map (other than an airport) it pops up a Quick View box with the lat-lon coordinates at the top of the box. Currently, that's in d-m-s format. If you're wanting to see lat-lon in decimal format in your Current Loc instrument then you probably also want to see it displayed that way in these popup boxes too I imagine.
BTW, you can use this feature to find your current location by tapping on your plane's icon on the map.
Now that I look for it, lat-lon coordinates are also displayed in the flight plan (if you have lat-lon waypoints), in the Airport Info screen (though it's displayed in both formats there currently), and probably other places. So, again, I think this should be a user-chosen global parameter that applies to everywhere lat-lon is shown.