There is a map mod on mapquest that is entirely hand-crafted. It didn't take any files from the game at all, and thus does not violate even the most strict interpretation of the TOS. (The TOS specifically refers to modifying any game files.)
However, the point of this thread is *not* that Cryptic doesn't want people using mods. That isn't the point at all. They simply don't want to be seen, in any legally arguable manner, to be supporting them in case someone does Something Bad (tm) that damages someone else's computer.
So I doubt they're going to do anything so offensive to the player base as to prevent people from using them. They're just covering their collective heinies from potential legal troubles down the road.