Well, my own list didn't include any southern mages. I had a laetan blood mage, a rivani seer(Rivain is relatively close so that wouldn't necessarily count as terribly exotic), and an ancient elf - partly as appeasement to the Abelas fans but also because I think that would be a good way to tie into the Solas plot.
I just don't think we're going to be hurting for Tevinter mage NPC's to get perspective from, so I'd like to see our party stacked with some more wide ranging options so we have the outsider's perspective as well.
This does fit with the DA track record; relatively few of our companions are native/local to the area the current game takes place in. Alistair, Wynne, and Loghain were the only ones native to Ferelden society in Origins, Varric and Sebastian were the only marchers in DA2. And in Inquisition, Vivienne and Cassandra were local to Orlais, and Sera was native to Ferelden, but everyone else hailed from regions we didn't explore in that game.
So I tried to keep it to two or three locals to fit that pattern.
This so much. All of the games have had the majority of the companions not be local to the game's regions. There are also a few other trends so far to party composition (not that DA4 can't deviate from that, but the devs seem fairly comfortable sticking to a relatively similar formula):
The "outsider" to the local area: Morrigan lives close to Ferelden but is not Fereldan. Plus she is an outsider to "civilized" society. Merrill, as a Dalish, fills the outsider to urban lifestyle slot.
. Each of these characters acts as a foil to the accepted status quo. Also focused on lost knowledge and magic.
The "adherent": Leliana, Sebastian, Cassandra. Not necessarily followers of religion as an institution but of their personal faith.
The "other": Shale as a free-willed golem, one of a kind and challenges centuries-old assumptions of knowledge. Anders, a possessed mage trying to balance two entities in one body without being completely subsumed by the spirit within. Fenris, to a lesser degree, with unique powers brought from lyrium which is normally toxic or fatal to people. Cole, again contradicting assumed knowledge of the nature of spirits and the Veil.
The "mentor": Wynne (obviously), Aveline, Vivienne. How much the PC appreciates or follow the mentor's advice varies, but the tone and relationship the mentor attempts to adopt with the PC lends itself to being in a position of authority and trying to guide the PC as they think is best.
I think there is a requirement for at least one Ferelden in every game, but luckily Harding covers that. And a maximum of a third of the recruitable companions being from the nation in which the game takes place.
So with all of this said, I think it's reasonable to expect something along the lines of:
Scout Harding (Fereldan, carry over from previous game)
Marius (cross promoting supplemental materials). This depends on his role in the comics, and what kind of fighting he uses, whether dual dagger or sword.
Laetus mage as others have said. I think anyone at the level of a magister is too powerful and busy to join the party. I'm ignoring the level one Cassandra issue. This mage would be the moderate voice of reform but not rebellion for Tevinter, as they have not had the roughest life and hope to rise in status, but they haven't had all of the opportunities that altus mages inherently possess. This might be the adherent, as I don't think we'll get a companion completely for the status quo of Tevinter life and religion, but someone who see the good possible (like Leliana does of the Chantry in DAO)
Tal vashoth of some kind. I would think a fighter would be easiest to implement, but former Ben Hassrath thief or rogue saarebas could work. A saarebas would fit the "other" role most likely, given how rare it would be to find an unleashed kossith mage who used to be under the Qun but purposefully left it. A non saarebas would fit the outsider role, as someone now in Tevinter and knowing a lot about the culture without being a part of it.
Ambassadoria dwarf fighter. I hope that we can get two dwarf companions again, as the ambassadoria culture in Tevinter sounds different than Orzammar and Kal Sharok and surface dwarves. The dwarf would be fairly positively inclined toward Tevinter, as the mages are a major source of revenue and treat the dwarves with respect. They could possibly be the mentor?
If we don't have a saarebas, then the "other" could be a Rivaini seer, awakened ancient elf, or a Warden from Weisshaupt (I'm wondering if the Anderfels will play a role in the game)
For the elves, I doubt we'll have any Dalish, since they're not supposed to venture north that much. Either a viddathari, ancient elf, former slave, or maybe even a rare mage who was raised beyond slave status for their talents. Fenris' sister, after being freed, was apprenticed to a magister, so there seems to be precedent.