Maybe it's more complex to get this to work, but why don't mix the first two?
At the moment of guild creation, it could give the possibility to stipulate how many leaders there will be, and who they will be. With a maximun of three or four person, for example.
So if someone want to be the only leader, he/she just select for 1 leader. and if their are two friends, select for 2 leaders, and so on.
If the actual leaders think a guild member is of confidence, and deserve to be a leader as well, they could discuss it, and open a new seat for him, giving him leader rights.
Or if they are 4 leaders, and one of them has to leave the guild (for whatever reason), he leaves the seat open. The other 3 leaders can decide if to close the seat, wait for the return of the fourth leader, or if the guild needs to have 4 leaders, the remaining ones can appoint one of the guild members to have the seat.
Dunno, it gives a lot of freedom to guild organization and management. Also, there could be a ranking structure inside the guild, subleaders, event organizers, who knows, maybe the guild could open a new branch and appoint a member as the leader of that branch. The guild Brassbolt opens a guild branch for aerial combat, where guild members who likes to be in the sky or are good for combat up ther reside, and the clan leader(s) appoint their best pilot as branch leader, managing it.
There should be limits to the numbers of branch that can be opened, and the guild should pass the requirements for doing so.
A crude diagram:

Uploaded with
ImageShack.usAnd the Main Clan and branches would have their own member, I mean, the main clan has a limit for 40 members, and each branch support another 20. This appeals for thos large guilds that just doesn't stop growing.
As for the internal structure of the guild, there could be:
-Guild Leader(s)
-Subleader(s)
-Officers
-Regulars
-Newcomers
Each rank would have their own rights, privileges , dutys and obligations, and the leader(s) would select what ranking suits a guild member. And who knows, maybe those could be the default names for the rankings, the leader(s) could change them to match the goal of the guild, if they are a battling/pvp guild, a merchanting guild, adventurers guild, researchers, etc. Depending of the ideals of the founders and members, and would give some roleplaying flavor.
Well look at this, I am rambling nonstop and surely I am boring you all to tears, I will shut up now xD
-Reivaj.
PS: Don't kill me for raising all these threads from the dead, it's just that as the more I read in the forum, the more ideas and things cross my mind ;_; maybe they are difficult to code/script, who knows, I don't know much about programing. Dunno why I am so talkative in this post. Oh and sorry if my English isn't that good

Yeah, I will go get my coffee :3 So... see you later
PS2: Silly me, I just saw that the changing of rank's names was addressed sometime ago, sorrry about that. *scratchs the back of his head*