Healers:
I think healers will mostly stay as it is, with one dot and one nuke, but they'll add even more healing bloat to the healers to make it even easier to heal any encounter optimally without any sort of planning required.
Tanks:
GNB and DRK have got to go. People complained about Gnashing Fang, so perhaps they will remove Continuation, so that GNB can just as easily move the boss during GF. DRK has too many oGCDs and that stressed players out, so they probably will remove some of them. However there isn't much left to dumb down on the tanks really.
Melees:
This will probably be gutted the most. Positionals will probably be removed.
MNK: I expect them to change Perfect Balance to 60s. This will render optimal drift completely obsolete and make the 2-min window significantly easier. They will probably also remove Riddle of Wind.
SAM: Kaiten will probably be back in all honesty, while they will gut down the rest of the job. Perhaps they'll just make Shoha into another cooldown. They might also make Ikishoten into a something that buffs the potency of Senei so you barely have to care about overcapping at all. Maybe they'll remove the different Sens completely and make them one single Sen so that you can literally press your fillers in any order and still win.
DRG: The rework is coming and I honestly expect it to be lobotomized into something like SMN. Now you'll summon different dragons and then press 1-2-3 in different styles. There will be no 4-5-1 anymore you understand, a 6-part combo is too long. You'll just summon Nidhogg's rage in the opener and Hraesvelgr in odd windows, then press 1-2-1-2-1-2 for 15 seconds.
NIN: Just change mudras to 30s. That alone will dumb down the job to unimaginable levels because you have now far more leeway to screw up your burst window.
RPR: I genuinely do not know how this can be even more dumbed down. Perhaps they will simply remove the Enshroud gauge altogether and make Enshroud a 60s cooldown. Double Enshroud and tracking two gauges is apparently too hard for players. So we'll force everyone to do single Enshroud.
Casters:
BLM: Yoshi P's blessing will stay with this job and it'll somehow still have transpose lines in 7.0, making it once again the only complex job.
SMN: I feel that there is nowhere for this job to go but up, but that is not guaranteed. Ruby Rite is too much of a hassle for phys ranged players cosplaying as casters though, so perhaps they'll make them instacasts, but with a 3s recast. Because SMN players need 3 seconds to fully think about a mechanic.
RDM: Dualcast will no longer be interrupted by actions other than GCDs. Everyone will praise this as much needed QoL. Moreover, cast times on Jolt and Verfire/Verstone will be shortened to 1.5s so you can very much feel free to weave anything in any GCD. Everyone will love this while Fleche and Contre Sixte optimization gets completely gutted silently without anyone noticing.
Phys Ranged:
What is there to even gut on these jobs now honestly?
MCH: You can now use Drill, AA and Chain Saw during Hypercharge without losing anything!! Hypercharge will simply last for 20s now you see.
BRD: What is there to really gut on this job now? I guess you could make Apex Arrow a cooldown.
DNC: Somehow DNC went from being the braindead phys ranged job when it launched to being possibly the hardest one in EW. Well, they'll simply give us an upgraded Saber Dance that gets procced by Standard Finish, just like Infuriate, and nerf Espirit generation so much that you have a million years to think about spending it before you overcap. And that new Saber Dance II will always give you Fan Dance so now your 2-min burst is pretty much static!