I had thought of doing this before the 1.2 patch, allowing the romans to recruit hastati, principe, and triarii early, ramping up the exp for the lower level troops as the barracks level increased. Not sure I would do it for peasants though.

Some people suggesting using other building requirements to give a exp bonus as well, but I think there were problems with that (both buildings had to have a recruitable unit???).

It's a good idea for some troop types, but not all. If a legionary cohort is buildable, why even give the early leg cohort option at a town? Retraining is all I can think of.