As Tuco said, the only official class left is Artificer I'm pretty sure. I think getting new subclasses would be entirely plausible since there's less (but not no) reactivity to subclass and most of it isn't major. A lot of it tends to be lines that our Tav can say, which is as simple as adding in some dialogue - thank goodness they didn't make Tav voiced. I think given the relatively decent reactivity and the options they offer, a DLC containing like, two or three new subclasses for every class would be a reasonablel bet. Not a given, but also not unrealistic.
On a side note, D&D 5e's approach of making everything a subclass is... interesting now I've looked at other alternatives. The way they've made various subclasses so varied and distinct within themselves has made it so that a new class really needs to have some strong central theming to justify not being a subclass. It's not necessarily bad, just an interesting choice.
