They'd probably have to rethink a lot of jobs if they got rid of positionals. There is a penalty for ranged physical DPS in the damage department. They don't worry about positionals and can do damage anywhere, so they can preposition for certain mechanics. Casters have a bit of a bonus to their damage since they have to be a turret and be clever and time the usage of abilities like Triplecast to move while keeping the uptime.

Removing positionals would pretty much take away half of the "difficulty" of playing a melee DPS. Then it would be about using your gap closers, etc to overcome the boss moving or getting out of the poop. In order to achieve balance, SE would have to put BLM at the top and move all the physical ranged to be almost on par with melee. I guess it could happen.