If it was me I'd avoid Noct AST. It's simply an inferior version of Diurnal and only serves as a necessity for low ilv prog. If things don't change much, shield healers will likely still be pure healers with bonus shields. Learning how to effectively pure heal on a "shield healer" and only use shields when necessary or they're free oGCD's will make you a better healer than going Noct to "learn shields" and blindly spamming AspHelios. For that reason Diurnal (which has Neutral and bubble mit) or SCH, and learning how to use the toolkit efficiently are probably your best choices.