You would have to cut Chillmaw. I don’t see room for another big dragon besides Chillmaw. Personally, I can see your point but don’t like Nozdormu. If you really want anything else than Chillmaw, Ysera is a nice pick. 4 attack means not easy to remove for other Priests. Other options are Nefarian, Alexstraza, Ragnaros or Deathwing. But honestly, Hotform knows what he’s doing, so Chillmaw has his purpose.

If you really want to replace Chillmaw, I highly recoomend Ysera or Book Wyrm. While Ragnaros is a popular card, this is a dragon deck. So you don’t want to switch out a dragon, for not a dragon. Ysera is absolutely nuts in the mirror (4 attack), Book Wyrm yet another body with removal. Entomb is just bad in this meta for Dragon Priest.