I doubt they would ever make a game that restricts you to one class.
By no means you should be restricted to one class, what I mean is that despite having magic you should be able to train as a warrior or a rogue.
It always bothered me that, while warriors and rogues can't become mages, there is no reasonable explanion as to why a magic users couldn't opt to develop mundane fighting skill rather than spells.
How is magic "overtaking all the lore"?
Elven gods were mages, Titans made dwarfs and can give them magic and immortality, the magic realm known as Fade was once one with the physical world and back then everyone were mages.
Back in DAO it was about dealing with political BS from different factions threatened by the blight while magic just popped in between, then we shifted focus to the mage-templar conflict only for that to be overtaken by ancient Tevinter magisters and then setting us against ancient elven demi-god mages.
Case in point we went from Loghain/Archdemon (mundane/magic) to Arishok/Meredith/Anders/Orsino (mundane/anti-magic/magic/magic) then to Corypheus/Nightmare/Samsom/Calpernia/Hakkon (magic/magic/anti-magic/magic/magic) and now we are going against Qunari/Tevinter/Solas/Evanuris/Titans/Blight (mundane/magic/magic/magic/magic/magic).
You mean a protagonist who only just recently found out about their status as a Mage? That would be interesting but it goes against lore. The power that comes with being a Mage manifests in adolescence and I find it hard to believe that it would go unnoticed into adulthood. Also, a Hedge Mage by definition is a Mage that wields powers developed outside "traditional" teachings.
Mage Hawke and Bethany were possibly technically Hedge Mages if you discount that they were taught by their Circle trained father. While one branch of Hedge Magic applies to Mages who are taught differently i.e Morrigan, the definition also applies to Mages who have no training at all such as Saarbas. In that case the Mages Magic apparently develops differently and they become incapable of casting Spells as other Mages do.
While this is an interesting concept that I hope is explored further I'm not sure it would work for a protagonist. It would require a completely different set of Spells and talents compared to other Mage Companions and would also, possibly, leave out the possibility of exploring "real" Blood Magic and Blight Magic, that is assuming that DA4 takes place in Tevinter and The Anderfels respectfully.
It's not impossible for people to discover their magic only in adulthood, Saarath grew up as an ashkaari (a philosopher) until his magic manifested into early adulthood and he was made into a Saarebas.
Commander Shepard is stated to have only shown biotics once he was already a soldier rather than at normal puberty age so there is a precedent for it to happen in both lore and in Bioware's protagonist profiling.
The point of having a hedge mage as protagonist is for him or her to perform feats of magic when the plot requires regardless of their game-play class without having to create another anchor to explain how the MC can use magic power regarless of their origins.