My impression as to why AST weren't favored for raiding is the subpar DPS. Whether they were limited solely by MP or also weaker nukes/fewer DPS options I don't know. I don't raid but I never really had MP problems nuking in normal content, but of course I never nuked over what I could handle MP-wise and I could never match the numbers my WHM could put out. Don't play SCH but I'm quite aware of how good it is and how hard it can DPS over both other healers. So unless new raid requires less DPS from healers (entirely possible actually considering it's not what SE wants from healers and they expressly stated they were easing up on DPS requirement) I still don't think AST would be favored... it will take quite a lot for it to hurdle the stigma it's got already too. But of course if Ewer and Spire got a lot better than they already were, I'm sure people will at least be considering it.
What I'm wondering now is if SE would have tuned Midas toward AST the way they tuned Thordan EX to PLD, just to give it a niche (which is basically waving a flag saying "look we make content that lets [X disfavored job] be relevant, too!")