Yeah, 5e "Paladin" combines all the prior edition classes which were "paladin but not LG" under one roof. In general I'd expect an in-universe use of "paladin" to still refer to the stereotypical knightly LG crusaders or at most the zealous, unforgiving LN types you might get from some Helmites. Whereas a class-paladin of say Sune might in-universe be referred to as "champion" rather than paladin.
But, I doubt we'll see subclasses outside the base game to start... much as I'd like to see all the subclasses and all the lineages.... I would prefer the game be able to get released in the next year or two and just have the rest as DLC.
That said, I do have an LG-ish idea for a Conquest paladin inspired a bit by Saber-Alter... even have some art for her somewhere.... and you can definitely tweak Vengeance paladin to do a blackguard...
