something tells me there will not be 3 new jobs.
three jobs would be uneven, since there's an even amount of jobs now. That would mean the "Job change" screen would have an unopen spot. Hence, the choice is between 2 or 4 jobs. 2 would mean they can't add what they want, since they always seem to add one melee job, one pet job and one support job.
RoZ had SMN as support/pet job, DRG as melee/pet, SAM as melee, and NIN as "support"/melee
ToAU had COR as melee/support, BLU as a bit of everything really, and PUP as pet job.
So logically, they either need to make 2 jobs that fit in to each of the categories similar to BLU, or add 4 jobs. 1 tank, 1 support, 1 pet and 1 melee. And it makes sense that they would add one to each city - Sandy, Windy, Bastok, and Tavnazia or Jeuno. I do believe Jeuno were only a small fishing town at this time, or were that further back in time? and I SE partially mentioned travelling to the old Tavnazia might be a possibility. So that leaves us with either Jeuno or Tavnazia as the 4th town.
Speaking of which, I'd love to see Windy while it were NOT flooded.
Either way, putting the jobs by their respective city, Sandy were and is a noble nation, and used to be one of the nations with strongest military power, and were raising the black Destriers as battle chocobos. Which, untill recently, had "died out". Windy, as always, is mostly trained in magic. Bastok is the typical mechanical nation. Hence, it makes sense that each of the three main nations would get a job fitting their theme.
Hence, we could get something like the following:
Sandy: Chocobo Knight
Bastok: Alchemist
Windy: Geomancer
Assuming SE does not want to make the number of jobs uneven, nor leave out one of the nations with a job, we have a 4th to add to this list. So either Jeuno, which don't really have a theme of itself and is mainly a trading/fishing town, it leaves us with Tavnazia. No idea what real "theme" this nation have, so it would possibly be one of the out-of-the-blue jobs like PUP.
What I find slightly surprising, is that supposedly, the siblings (the boy and girl) from the intro video, according to SE, were involved in the CoP storyline somewhere in some way, but I can't remember ever seeing either of them. And the girl supposedly died.
Either way, Tavnazia used to be connected to the mainland, so I believe there's a high possibility that this will be the new "capital", like Jeuno and Aht Urhgan White Gate before. SE also said that you could possibly meet them again in this expansion, which hints that going to Tavnazia is possible.
I can't personally remember ever seeing the boy from the intro video. I also haven't personally done the quest he's involved in. However, the necromancer from the quest is involved in the mannequin quest. He agrees to breathe life in to the mannequin in order to bring back his beloved Alsha.
Dialog Table Entry 00660 Ah, I see your preparations are complete.≺Prompt≻
Dialog Table Entry 00661 Y-yes...
L-let us b-begin...quickly!≺Prompt≻
Dialog Table Entry 00662 Relax, my troubled Enaremand. All shall be realized in due time. One cannot rush the flow of the eternal lifestream.≺Prompt≻
Dialog Table Entry 00663 ...
The spirits will answer our call when they are ready.
...Despite whether we are or not...≺Prompt≻
Dialog Table Entry 00664 Are you ready, my friends?≺Prompt≻
Dialog Table Entry 00665 ≺Player Name≻.
Please place the ≺Key Item Parameter 0≻ here.≺Prompt≻
Dialog Table Entry 00666 Now.
Let us see what angel floats down from the clouds of Paradise...≺Prompt≻
Dialog Table Entry 00667 Or what beast treads forth from the ichor of the Styx...≺Prompt≻
Dialog Table Entry 00668 P-please... By the light of Altana...!≺Prompt≻
Dialog Table Entry 00669 A-Alsha!≺Prompt≻
Dialog Table Entry 00670 As I expected...
≺Player Name≻! You know what you must do! But be swift!≺Prompt≻
Dialog Table Entry 00671 You place the ≺Key Item Parameter 0≻ gently on the ground.≺Prompt≻
Dialog Table Entry 00672 M-m-m-my...m-m-m-my beloved Alsha...≺Prompt≻
Dialog Table Entry 00673 W-what have you done! Y-you m-m-m-monster!≺Prompt≻
Dialog Table Entry 00674 Enaremand...
Do you still not realize?≺Prompt≻
Dialog Table Entry 00675 It is not ≺Player Name≻ who is the m-m-m-monster.≺Prompt≻
Dialog Table Entry 00676 B-but Alsha... Sh-she w-was... Sh-she was...≺Prompt≻
Dialog Table Entry 00677 She was nothing more than a puppet--a crude golem pieced together from sticks and clay. She was not your Alsha.≺Prompt≻
Dialog Table Entry 00678 Y-you don't understand! Y-you don't know the hell I've experienced these past t-twenty years. The hell I'm in now!≺Prompt≻
Dialog Table Entry 00679 But what did you expect by knocking on the gates of the underworld?≺Prompt≻
Dialog Table Entry 00680 I warned you, my friend...≺Prompt≻
Dialog Table Entry 00681 I...
There is n-nothing left for m-m-m-me in this world... Curse you, Altana!
Come, darkness. Take m-m-m-me to your kingdom!≺Prompt≻
Dialog Table Entry 00682 The infernal mists have lifted...≺Prompt≻
Dialog Table Entry 00683 ...≺Prompt≻
Dialog Table Entry 00684 ......!≺Prompt≻
Dialog Table Entry 00685 Alsha!≺Prompt≻
Dialog Table Entry 00686 I...
You...≺Prompt≻
Dialog Table Entry 00687 S-so beautiful...
Nothing like m-my m-mannequin...≺Prompt≻
Dialog Table Entry 00688 Oh...
I'm so sorry, Alsha.
What was I thinking?≺Prompt≻
Dialog Table Entry 00689 I knew all along that I could never replace you...recreate you. But I was so lost...≺Prompt≻
Dialog Table Entry 00690 Perhaps if I had just looked harder...I would have found you...≺Prompt≻
Dialog Table Entry 00691 Right here, in my heart...≺Prompt≻
As you can see, she's been dead for 20 years, and he's strived to find a way to bring her back to life. That means she most likely died during the crystal war 20 years ago, which is the time this expansion takes us back to, no? Which means we'll likely see this NPC in the past.
Now, back to who he might be. I haven't personally seen this NPC, but possibly he might be the boy from the intro vid. Or he's someone completely unrelated.
Either way, it hints towards Tavnazia being one of the towns we get to visit, and possibly Necromancer being the last job. That boy had to have learnt it from somewhere.
edit: its completely possible we only get 2 jobs, both given in Tavnazia as well. I somehow find 3 unlikely though.