I think it would be great if certain skills were mutually exclusive from other skills. For example, if you wanted to be the very best crafter you couldn't have top skills in mining or gardening. In other words as new skills are added and, maybe, higher levels of current skills you would have to choose which path you wanted to follow. With a number of different kinds of specialists Ur would become a more interesting place and the kinds of interactions would multiply. The fact that we can have every last skill and do everything for ourselves seems to run counter to the idea of promoting a variety of social interactions. Also, this would make unlearning much more important so that you could specialize in one area until you tired of it, unlearn those skills and try out a new skill path. Taking the skills one at a time in this way would be another way to extend the amount of playing time before you had tried everything. But mostly I just like the idea of specializing.