What if Aizen's Grand Father/Relative Had to get the position of soul king but the present soul king managed to steal the position.This explains why Aizen wants the soul king position and also his statement "he doesnt deserve his position" (some what like that)
If your theory is right he will most probably get beaten up by the fully devloped SR at the beginning and then he will get a power up and own the SR.Most probably after the fight he will get owned by another SR.(Just like in Hueco Mundo)
After Full Bring Arc,Chad and his powers has been ignored.Will he get anymore powers?
I also think he an underrated character.He should get more attention in the manga.Chad vs Gantenbainne was a good one but it's the only real fight Chad gets in the ENTIRE series
I hope Tite Kubo gives him...
Mayuri did experiments on quincies way before,he also tells ishida that he did experiments on his grand dad.Maybe Mayuri is bringing a experimented quincy or Ishida's Grand dad back? :blink