I think the Storm Sorcerer is most likely to be there, just an updated version from UA.
The Favoured Soul was also a nice subclass, but perhaps it is a bit too awkward concept both narratively (deviates a lot from the sorcerer 'inborn magic' idea, gets very close to cleric) and functionally by getting sorcerer spells + extra attacks + healing spells.
I wouldn't mind having the FS checked up for balance and released in a book, I'm just saying it's quite an oddball and as such I'd rather have something more 'normal' from the first real players supplement. For instance, a vanilla Elemental Sorcerer would be more useful, considering that draconic, chaos mage, storm and favored soul are all quite a lot specific concepts IMO (although storm is the closest to being generic).