The only issue I could have seen from this is the whole "Skyrim isn't based on classes". But that's easily solved by, say, having hte college say "To properly earn the resepect of the college, and to attain archmage, you must have at least a 90 in one of the following schools: destruction, etc, etc." Because what is an archmage that can only cast frostbite for 10 seconds? Not much, in the bigger scheme of things.
All in all, I'm just musing on how the guilds could have *seemed* to be more in depth, to have that feeling of working towards a rank, that I feel they lack. I'm not saying they should add anything like it to skyrim now, that'd be silly. But would it be a feature you'd like to see comeback in later elder scrolls games?