I sincerely doubt they'll give us a new class with a Chapter each year. Maybe another class will come in 2019 or potentially 2020. A new class would be a lot of work, and my understanding is that the Warden was considered a potential class before release and the spells for the new Warden class came largely from that work and the shelved Spellcrafting development. Odds are good an absolutely new class would be a much more significant project.
So chances are, next year, ZOS will add something to the game akin to a vampire/werewolf skill line to justify dubbing the content a "chapter" instead of a DLC. They may also finally add jewelry crafting. Lots of other big "upgrades" to the game will do.
What I've been considering is something inspired by an idea I read on another post on a forum poll. Somebody talked extensively about a concept he called "prestige" or master class, which is unlocked at some point after a character has been thoroughly developed. A prestige or master class would be different than vampire & werewolf, which are available to a character at level of progression. It offers a better incentive to keep playing than Champion Points because it would mean opening up new spells and skills. And I thought it was a cool idea for that reason.
My understanding from the post I read was that new abilities would be created for this purpose. And that's certainly a possibility, albeit a tall order from a development standpoint.
However, I had something different in mind.
Let an existing character learn a Subclass Skill Line from another class.
Currently, we have five classes, each with three skill lines. What if the game was changed such that a sufficiently developed character (the criteria for which, I'm not sure about) could "learn" a new skill line from another class? In fact, that could be the qualifying criteria -- the character learning the skill line must be high level and the character from which it is learned must also have that skill line maxed-out.
Just an idea. It would be a cheap way for ZOS to add something interesting to the game without needing to create all new skills and abilities to achieve it.
It may lead to some balancing issues as certain class/subclass combinations rise to become the "new meta" or "best-in-show" builds. Or it may finally put character development into a realm in which there are too many possibilities to explore for that to happen too often.
As it stands, there are 10 races, 5 classes, and presumably only 2 viable builds, magic or stamina (I wish hybrid builds were better respected, but alas, that's a community decision). You can be a vampire, a werewolf, or none, so that's choice for which a player has 3 options. So that means, currently, there are 10 x 5 x 2 x 3, or 300 possible builds.
Consider how many potential builds there would be if any class could learn ONE skill line from the others. Five classes, each with three skill lines. A given character would have a chance to learn any one of the three skill lines from the other four classes, opening up 12 more opportunities to diversify that character's build.
The new formula would become 10 x 5 x 2 x 3 x 12, or 3600 possible builds.
Add another werewolf/vampire transformation after that (maybe in 2019), we have 10 x 5 x 2 x 4 x 12, or 4800 possible builds.
And if they add a sixth class after that (maybe in 2020), the formula becomes 10 x 6 x 2 x 4 x 15, or 7200 possible builds.
Expanding the number of viable builds from 300 to 3600 (or 7200) could go a long way to mitigating the rise of cancer builds. Allowing an existing character to learn a subclass would also satisfy some of the calls there have been for a "class change" token.
That's my idea. It would add more diversity and character progression potential that the Champion System failed to deliver. Sure, it felt good spending points on the new passives after the Champion System was introduced... ...for a while. But now I've hit the cap and far exceeded it. Allowing max-level characters to unlock a subclass skill line from one of the other four classes would, quite literally, give us something else to play with.
Someone could give the storm calling Sorcerer skill line to a Dragon Knight wielding a frost staff and role-play as The Avatar (Aang or Korra, your choice).
Someone could give the restoring light Templar skill line to a Warden and finally make them into respectable healers. ;-)
Consider the possibilities. It would add a lot to the game (and do so cheaply for the development team) and would be a significant enough change to justify doing it in a Chapter content release. It would certainly guarantee everyone buys that Chapter, regardless of whatever new zone, dungeons, or trials. It might even attract people back to the game who exceeded the CP cap, got bored, and drifted away from the game.
Just an idea.