There is already the possibility to toggle fog of war on/off, which is actually mostly the same that you are suggesting. This is used regularly by casters to see if someone sees sneaks, units or hidden ressources.
I guess you suggest that one can see the range of a unit with fog of war off, where I don't see the benefit for casting purposes. Maybe you could elaborate on that because I don't see it (no pun intended).
No, what im looking for is a circle around the unit/building.
I don't know how I can elaborate on that, honestly but I guess it's a nice addition which gives clearer informations.