Question from a new player - can AST change back to what it was before ?

[Risvertasashi]

Typically major changes take a new expansion, with only relatively minor changes (potencies, cast times, maybe an overhaul to a single ability, etc) available during the normal patch cycles.

As for if the old system will ever return? I highly doubt it, but I've been wrong plenty of times.

Things looked pretty bleak for Bard in Heavensward too, with a number of people believing we'd be stuck with "bard mage" indefinitely. But the dev team did relent with Stormblood.

So, with enough feedback it's definitely possible. But it won't be quick.