The amount of time required to implement this feature (both in terms of programming and art) and the low return (basically it isn't a feature that everyone would want/use) is why its never really been anything we've put effort into, either from a planning or development perspective.
Because of the size of our team (and not just at present, but going back all the way to late-2004) we've had to be careful with the things we choose to develop. We typically focus on things that have a high return, such as high-level content, low-level content, performance improvements, plot/lair art, and that sort of thing. These things have a high return because they either a) appeal to the long-term folks, b) appeal to new players, or c) are for plots and thus appeal to just about anyone.