current thoughts based off of what little we know about healers specifically:
I've heard that Astrologians are unable to change stances mid-battle - this is a very, very silly design decision and I hope it gets reversed. This basically pigeon-holes them as "replacement healer" since their jack of all trades nature seems to indicate that their abilities are actually categorically
worse
than most of the other healers' abilities (it's likely their regen effects, for example, will be too weak to make them a full WHM replacement with spspd affecting HoT effects, and their shields will likely be weaker than a SCH's). That being said, their adaptability will make them the "if you for some reason can only play one healer class and you want to solo heal things once you out-gear/skill them" go-to.
From a WHM's perspective, the only things we can really conjecture off of are the spellspeed changes (will likely make spellspeed #1 optimal stat for all builds instead of being for solo heal builds, especially with the refresh effect on Assize), and the changes to Holy and Assize (which we have numbers on). Holy is getting absolutely and 100% eviscerated, and is Squeenix saying "fuck you WHMs in speedruns/DD first room/etc". Assize is a 90s cd with a 300 heal potency, making it not really that great except in emergency situations (not what we were hoping for - the ideal would be an instant-cast at a large mana cost, which is what i was expecting) and massive AoE spikes (a swifted Cure3 + Assize will equal 850 potency in heals out in a split-second) a la Gigaflare/Rage of Bahamut/Megaflare/etc.