I think its a bad idea because the whole point of leveling is to get to know your class and skills. a trooper can be heals, tank or dps, i think that if you had the option to play any of the three you would not learn how to do any one well. The first 10 levels are a throw away to get you use to the game, in which point you evolve and decide what path you want to take. If you're going to allow advanced class changes then you should just allow complete class changes because its the same god damn thing. You are something but you dont want to be that something so you wana be something else now.
Class changes are bad news because it only encourages badies to keep being badies instead of trying to learn the game through practice. You'll never get good at anything if you dont practice at it. Plus bioware has made it so damn easy to level an alt its sick so just level a god damn alt already so you can raid in 2 guilds instead of one.