That could have been a really strong storyline definitely. I think season 6 especially suffered from Dawn feeling a bit like an afterthought because she was younger than the other characters, and so couldn't feel like part of the gang in the same way. Episodes focused on Dawn like All The Way almost felt like their own spin-off because Dawn and her friends were part of a completely different social circle. Maybe she would have worked better as a recurring character after season 5, like Joyce. There just weren't a ton of interesting storylines they could use for a little sister character