Excellent post Seriha.
I'm gonna approach my guesses from an MtG perspective of 'filling gaps' and 'cycles', which is looking at it from a slightly different perspective overall. This is also taking into account that Yoshi-P said we would be getting hybrid/support (thus completing the 2/2/2/2 model), because any new job you have to immediately think what does it offer vs. an existing job for incentive to replace (in addition to any Hybrid/support jobs, since they will be replacing 2 dps).
Ranged Attack
Blm is magical ranged dps, Brd is currently physical. In an ideal world Brd is moved to Hybrid/Support (with a possible changeup of abilities, I know the playerbase would riot) and Ranger/Hunter branches from Archer as the physical ranged dps. It should have significant DPS abilities w/virtually no party support ala Blm.
Ranged Support/Hybrid
If we move Bard to physical ranged support, then you have a 'gap' of magical ranged support. Since we actually have 2 ranged magical dps, Smn and Blm, I say move Smn to Hybrid/Support (and lo, there were many cries from the playerbase). Refocus it on debuffs and dots as it's 'support' mechanism vs Brd party buffing. I would actually swap a few abilities between Smn and Blm (Lethargy comes to mine, Apoc, plus buff it) to more realign the focus. Since ACN was so developed with Smn/Sch in mind, their general utility shows. Might as well make it official.
Healers
We have 2 magic based healers, both range based. I too would like to see Dancer branch off from Pugilist, which would add both a 'melee' based and non magic based healer. While being vulnerable to stuns and mob based AoE, it would have a strength in being immune to silence effects and if it is a samba effect like FFXI, it works to partially mitigate paralysis effects in that even if the Dancer is paralyzed, the other melee will still gain HP. Additionally, a samba effect could potentially allow dps to 'heal through' mob centered AoE as well by continuing to gain life as they dps, thus helping dps not have to lose rotations due to positioning and running. This would also serve to make autoattack kinda worth something lol. Waltzes could AoE as usual so stacking strats would exist and the dancer could heal ranged party members as well. In my mind, even though we have 2 magic healers and 1 melee, it would be better to look at the healer 'cycle' as to their effective range:
Whm: Ranged
Sch: Ranged/Close (due to pet placement and AoE buffs)
Dnc: Close
A final option for healer is Chemist. Give it a gun, let it branch from any engineer job. It can toss potions on a much smaller cooldown in addition to buffing the potency of heals (think Convalescence for other part members). I know people are against a job where money = win, but the idea of an Item-based healer as opposed to a spell based healer is very intriguing to me (similar to Ninja, we will get to that in a moment). Again, it would avoid silence effects and not require MP management. Tossing in the ability Mix for party defensive abilities and a tiny amount of dps ala Whm, if done right, I think this could be a very intriguing concept. Then every healer would be range based.
Melee/Physical
We have 2 melee physical tanks and 2 melee physcial dps (semi-discounting the Marauder dps builds and War dps builds, since they are more fringe as opposed to dedicated strategies). Starting with tanks, a ranged tank is something that I don't think is any type of viability so a magic tank is what is missing from the 'cycle'.
Enter Ninja.
Ok, for those of you who haven't immediately just left the thread, hear me out. Yes, Utsusemi was beyond broken. As we all know, Ninja was never meant to be a tank; it was meant to be a consumable class. Throwing and spells aka dps, protection and debuffs. Again, an item based spell caster is a unique concept that if done right, offers incentives beyond a traditional spellcaster, similar to Chemist. A magic based tank that doesn't rely on MP. Now, currently Paladin really only uses Flash for magic hate management, no curing or anything else similar to how FFXI Paladin played. War can use Flash as well but it's hate management is damage and skill based.Looking at it like this:
War: skills
Pld: magic and skills
Nin: magic
Ninja can serve as a completely different style of tank (again, we need to incentivize a reason to play it). While I certainly wouldn't want to see Utsu back, an evasion style, magic based tank is certainly something fresh and new. Having a spell rotation instead of a 'combo' that you stick to would be different, as you don't have to worry about resetting your combo if you have to stick a different spell. Again, like Chemist above, we run into the problem of money = win or even worse, that Ninja solely has to spend money to be effective. A partial mitigation for that could be having certain spells cross class for every class/job, thus the need for anyone to have tools on them at any given time is increased (similar to how anyone could have /37 Nin in FFXI and it was a good thing). At the worst, in a Full Party setup, Ninja would serve as an excellent off tank for those who believe that a purely evasion style, spell based tank would just eat it if a hit actually got through (Rune Fencer anyone?).
Moving to melee dps, we currently have 2 physical so we are missing magic melee. This role I could see being fulfilled by either Drk or Rdm (Drk would need a bit more adjustment to be more magic based). Either one would feel perfectly natural branching off Gld. Again, similar to Pld, both jobs would require TP and MP management for full effect (these jobs would moreso require MP management than Pld) . Drk could easily be added to the gld/mar/lnc sets, while Rdm could use either the magic all classes gear or the Disciple of War gear to full effect. En spells, personal buffs to increase damage like haste and dots (think Gld 30 Acn 15 and add Rdm to the dot spells). The insta cast dots would probably be best as they would allow Rdm to maintain its movement up close.
Drk could potentially come off of Mrd as well. Again, to be more magic melee, its skillset could include spells similar to how Cecil worked in FFIV. In addition, the Drain/Aspi/rAbsorb TP (why didn't this have a correct name again?) line could be added, as well Endark. The Absorb line could also have a dot attached (Absorb-Str would be a pretty damn good spell in this game). Having the Absorb line would also mean that Drk could be a melee class that doesn't have Str as it's primary stat (max Int for better Absorb-Str returns and the spell could put you about par with melee dps).
The main incentive to these jobs vs Drg and Mnk is that they are not position based; the balancing factor would be vulnerability to silence effects and again, having to manage both TP and MP properly for full effect.
Moving to the idea of support/hybrid, we don't have melee physical support. Having a Rogue class that branches into Thf and Nin seems logical; Thf gives us hate management tools form FFXI, in addition to enemy debuffs up close. This is your stun abilities, hamstring, etc. I would add this job and make it heavily position based: front/flank/rear skills. To balance this, I would give its debuffs very short cooldowns ala a very short duration stun off GCD with a short timer that can only be rear performed. Then you position front and flank abilities that are very good so that way you don't have people abusing a Thf just sitting behind the mob all day (if there is one thing FFXI taught me, it's that Thieves don't take too well to being invited for a single skill.....Treasure Hunter anyone?). This keeps the Thf nimble and constantly moving and giving you a lot of different rotations to perform.
To me, the Armoury System isn't the limiting factor, it's actually the Class/Job system. If Rdm came off of Gld 30 Acn 15, what's it's tertiary class? Thm? Cnj? In addition to that, could you come up with 5 skills/spells from 30 onwards that would really make a Rdm unique? Same for Drk coming off of Mrd. If we added a new Rogue class, it's easy to have a lot of overlap for Thf and Nin then 5 skills that really set them apart. The design corner here is more the ACN to SMN/SCH mold has really set a lot of expectations on what people expect (and even Yoshi has hinted that this model is one they would like to follow). ACN isn't really a 'main class' like how Gld is for Pld. Unless SE significantly retools classes to be much more varied like how ACN is (which in all honestly, classes should be much more generic than they currently are), this is always going to be the biggest limit in my mind.
Tl;dr
Arc = Brd (support) Rng (dps)
Acn = Sch (healer) Smn (support)
Rog = Nin (tank) Thf (support)
Eng = Chm (healer) ??? (????)
Gld = Pld (tank) Rdm/Drk (dps)
Mrd = War (tank) Drk (dps)
Thm = Blm (dps)
Cnj = Whm (healer)
Pug = Mnk (dps) Dnc (healer)
Lnc = Drg (dps)
Giving us:
Tanks 3 (War, Nin, Pld)
Healers 3/4 (Whm, Sch, Dnc/Chm)
Dps 5 (Rdm, Drk, Mnk, Drg, Rng)
Support 3 (Brd, Thf, Smn)
That looks pretty legit to me. Far form perfect but it has a variety of melee vs ranged, physical vs magical, positional vs anywhere to accommodate quite a few playstyles.