This was quite recent when I was just talking with people in the Balance Discord today, and I didn't even begin to think about how they're changing things until now.
It might be old news, but I think I have an idea of what they actually have in mind for changing the Healing Paradigm that apparently is mostly DPS(which is what optimized players should still be doing. Not saying DPSing is a bad thing, but it's something most people should do so they aren't standing there doing nothing unless long-term plans require more MP at a certain point).
WHM
As much as people have been saying that Afflatus Heals are just pretty bad and "more of the same"(which it is) I've had someone remind me of how WHM got kicked out of prog early on into Stormblood after Deltascape because of the constant AST buffs SE was giving them. What I realized was that WHM is now back in Prog in regards to how it was used back then. I think this is a good thing and doesn't make WHM so undesirable in groups since you have something to fall back on in case shit hits the fan considering they literally have the best MP economy with Thin Air right now, and Lucid being the CD for every healer to recover MP at a set rate.
The Afflatus Skillset, however, when used in place of your MP-based heals, gives you mileage towards Afflatus Misery and helps mitigate the DPS loss that you're getting from using a heal on GCD, and being Instant makes WHM able to weave freely Assize so there shouldn't be too many clipping problems now.
AST
AST...has gone through a lot of changes. Plenty of people on the forums already hate that they're taking away the complexity of the cards, as well as Spread and Royal Road that were used for planning ahead in fights. Considering that they were reduced to Melee or Ranged Buffs, people wanted their diversity back; but let us remember before why balance was literally thrown out the window: AST's constant buffing, and SCH never being knocked down off its high horse as king of raid healing.
With the Shadowbringers iteration, AST has a new skillset that requires them to draw 3 different Seals for their new skill, Divination, which is a 5% Raid-wide Damage buff if you draw all three seals. How they obtain seals is by playing the correct card that corresponds to that seal. Given that it is a 1/3rd chance of obtaining any type of seal per draw, that's why you have Sleeve Draw to make a sort of "burst" in your buffing. However, since you're trying to obtain a new seal each time and don't want to mess up your seal combo, you have Minor Arcana to eat up your cards if it's the wrong type of Seal. This creates a mini-game of drawing cards every 30s(with a burst every 3m) to attempt to get all three different seals for Divination.
Another fun thing is that Redraw is getting 3 Charges. This means that If you're trying to get the right seal, you can simply use it as a mulligan to find the card you need for Divination. While this does seem boring, this keeps AST busy as much as it does now, especially when it's also using Horoscope to enhance its healing potential in case things get hairy. Since its Healing isn't polarizing WHM through Sects anymore, it makes healers feel a bit more balanced in regards to how they all play around each other.
SCH
Now, for the best class of just about every expansion for last: Scholar. I had to take a long look at Scholar's kit to understand what the developers were going for, especially in regards to how they were to approach the problem that SCH caused for both AST/WHM; The Fairy, as well as SCH's Critlo Spread Combo which was heavily used ever since inception of Deployment Tactics.
How they did this was changing how Shields worked. Adlo now has a buff on a Crit called Catalyze, which adds Shield equal to 100% of the HP Restored. The fix to the Spread Combo was to reduce SCH's contribution to the raid by preventing raid-wide damage(which it can still do, but not as stupidly strong as they are currently, being able to stop a Savage Delta Attack in O11S with no use of LB Gauge). This still incentivizes Deployment Tactics' main use, which is to put it on a Tank that has Convalescence/Nature's Minne on them, and then spread it to the party; but now it isn't basically a 200% Crit Shield based on the healing done for the entire raid, but 225% for the target since Catalyze is not able to be spread across the entire raid.
As for the Fairy, a few adjustments had to be done so that pet jobs weren't so difficult to play for the newer players, but not so infuriating when you try to queue something and they just...cast whatever they're doing, and then do what you ask them to. The fixes to the summons and their casts being Instant helped alleviate A LOT of issues that the Pet System had in its previous iterations, however not a lot of people are happy to see Selene basically be a "skin" for Eos.
In my opinion, I want to think that the developers were having a difficult time creating unique decisions between Eos and Selene, given the fact that Selene's kit wasn't even close to competitive with Eos while also not overpowering the Fairy to where it was in Heavensward; this way, people can have both Eos and Selene which are tied into SCH's storyline and open up their options in both adjusting SCH's contributions and the Fairy's contributions.
Now from what I've read on the forums in regards to SCH's Aetherflow, people have been wanting a DPS ability that would allow them to dump excess Aetherflow. I used to be one of the people who wanted Energy Drain back(without MP Recovery) so that SCH could do its job again, but I then thought: "What if you're supposed to use those with Ruin II, which is 200 potency in Shadowbringers?" That opened up a whole new world of possibilities, and considering the 60s CD and how just about every confident tank under the sun has the "pull everything" mentality, SCH will probably use up those Aetherflows rather quick on Excog, Lustrate, Indomitability, or Sacred Soil(which has a Regen Effect to be competitive vs. Asylum). This also translates into how they will gain their gauge, and in turn allow them to use Fey Union for whatever duration they want; but in general I don't think that SCH needs Energy Drain back as much as people THINK they should have it back because of MP issues that people have foreseen because of DPS constraints.
While on the topic of DPS, Art of War has also been a topic of discussion, and how there's a demand for its MP Cost to go down due to it being 800/10,000 MP for an AoE spell. Generally I think it comes in line with the likes of Holy, but a lot of what SCH did before was abuse Miasma II for oGCDs instead of Ruin II. With the removal of Miasma II, SCH will still be able to weave for a decent potency once they learn Ruin II while also not having to worry about DoTs being their main damage next to Broil. Art of War is there to replace the damage that Miasma II would have done, but make it instant. It balances out with the rest of the kit since Aetherflow can be used for just about anything in 60s(and generally can be used to replace Physicks you'd otherwise be casting or Fey Blessing) and in regards to the overlying MP Issue that people exacerbate, that's why they made Aetherflow more focused on healing aspects in the first place and the trait Quickened Aetherflow synergizes with that rather well, potentially allowing you to have more resources earlier than you'd think once you've used up those stacks.
As for how the Fairy will act, we'll have to see how it works out when Early Access begins since we don't have control over her anymore. It's at least simplified better so that pets aren't a pain in the butt and die to Kefka's Hyperdrive(RIP Fairy) or don't listen.
End Word
For those who read this far, I'm willing to take criticism...which I feel may be overwhelmingly negative considering the nature of the Healer Forum right now, but I'm looking to be constructive. Even if Shadowbringers is 9 days away, just the thought provoking idea in the design is great and completely changes everything about how the game is played at an optimal level compared to how we currently play it now(which is DPS everything, try to always use Stacks on Energy Drain if not needed for anything else, Spread Balance, etc.). I can't wait to see how things unravel when we get the patch notes for Shadowbringers.