Line inputs are a waste of space in a keyboard WITHOUT speakers. Why put a line INto NOWHERE? That's what mixers are for.
As for Balanced vs UNbalanced line outs .... C'Mon man .... that's not a Pro or NONpro issue. It's a question of practicallity. Most users plug into mixers or snakes or PA's that are within a reasonable distance. The concert setups that require LOOOOOONg cable runs are what DI's are made for. No keyboard manufacturer is building instruments for EVERY possible application. Simple fact is: Balanced outs are NOT neccesary, and line inputs are best coupled with a sound system and speakers.