A major character being Tempered and needing to be put down as a result would serve to make the Primals feel like more of a threat. At the moment they...don't really feel too dangerous in my opinion. Sure, they may kill/Temper a bunch of nameless NPC's but there's no real connection between our character and those nameless NPC's. Yet if someone like Cid were to be Tempered by Alexander...then that would make him feel like a major danger. What we saw in Coil made me feel like there was a lot at stake - so it'd be nice to feel the same way about Alexander.