I think this has been brought up before and I like the idea with certain restriction.
I like the idea of the it being a choice but would be highly against it if it were mandatory.
I wouldn't want a league being locked down if there is not a co-admin assigned or a random person auto-assigned. Ya gotta really trust who your allowing to help run your league.
Also to go along with your pecking order, having the league owner be able to assign different admin privileges would be necessary. Such as team ownership approval, trade rejection, forums, GM removal, changing league titles and settings to name a few. The pecking order can be used if the league owner quits MFN for whatever reason.
Although this all sounds good for us playing the game, it might be tough to do on the programming side of things idk. That's for others to chime in that are way smarter than me.