It needs to leave the helm slot. Losing Perdition/Harlequinn for a skill that doesn’t have very significant aspects, and some aspects that are just underwhelming (Armageddon, and even Shattered Stars is questionable), is not a very compelling prospect.
If it leaves the helm slot, it now likely competes with offensive aspects, and needs an even larger damage boost (against something like Three Curses). It shouldn’t go in the chest slot because then it prevents you from getting Tyrael’s, and that would be a non-starter. I probably wouldn’t be opposed to putting it in the boots slot because there are no good sources of damage there, and Meteor lacks any other significant uniques. This would effectively make meteor unique in that one of its main sources of damage is a slot that doesn’t normally give significant damage.
I’m like 90% sure buffing the skill’s base damage is only going to affect the leveling experience with it. Meteorites seems to be the way we’re supposed to buff its damage but they’re just a very underwhelming source.
It just doesn’t have anything like Fractured Winterglass to massively buff its damage. Starfall Coronet is not it, especially with the cooldown. Raising the charge count is unlikely to do anything except make it better at clearing rooms, but does nothing against bosses, where it struggles the hardest.
As it stands, the only way Starfall Coronet can ever make it as a helm slot item is if it becomes a mythic unique.