There's also the thing to consider that not everyone in a clan is eager to take on the clan leader's job. So the nominated member would also have to want to take over.
And I agree with Russ that it would end up in tears. Imagine someone who's founded a clan and devoted time to recruiting members, and maybe even put up a website, suddenly getting the clan "taken over" by some charismatic, discustingly likable, ruthless newbie.
I do see a situation where a clan should be able to switch leaders - if the leader disappears off the site for a long time, without letting anyone know, and can't be gotten in touch with. But I don't think any real changes need to be made for that contingency - in such a case I think the clan members could probably just decide on the new leader and contact Russ about making a switch.