Eh, alternate sculpts is kind of a whole logistical thing, like Caimheul says. Given how Legion is marketed, it's probably not in it for FFG for the upfront trouble and cost of designing an additional sculpt, getting the molds, clustering up the production run when you can both paint around them, or just suck up your "screen accurate" units can sometimes look out of place. Rarely stopped anything Star Wars.
FFG is much better off spending those resources on making new whole units/packs, which are probably both more profitable and useful to the game. Since "Emplacement Trooper" is now a whole category, I'm sure that eventually more options will be added which can favor other trooper looks. Like if they ever get around to like the E-WEM turrets from TFU, those might be manned by Scout Troopers.