DM-4180 is scheduled for summer 2016; I wonder if you want to wait that long?
Much is changing in butler-land over the next few months, tho I can't say exactly what classes/methods (yet). If you're going to put new methods into CameraMapper that might be ok. It might be safer to add a common base class that you all can share
Either way please keep me in the loop about what changes you are making in butler and let's coordinate work as appropriate.