The engine is brand new, just keep it till it breaks. The money to swap in another engine and make the car RWD could be better spent on a custom turbo application. Build up internals, get some good fuel management, and you should be good to go. However, these are pretty much brand new so i'm not too sure if they make any real good aftermarket for it as far as engine internals go (TRD doesn't count...factory aftermarket? They bum off the real "aftermarket" and double the prices just so you can get the SCION name).
Mind you, i don't even own one of these ^_^ Wish i did tho, i love toyotas!~