i don't completely disagree with the premise around your idea, but don't see it being able to work on a long term basis.

the only reason i say this is you will not go to multiple cities on a daily basis. that means if i am concentrating on classes in uldah then i would not be going to limsa nor grid at that time. that would lead to me only taking care of one retainer during the time i am there. i usually go to the city that houses the guild of the class i am working on at that time. i usually don't leave that city for days at a time.