Right now, level requirements are about the best way to guarantee you can’t get a class until slightly further into the game. There’s also the class talismans, but when they’re made by the same class that can be promoted (herbalist → cleric, blacksmith → engineer), they have about the same effect. And when it’s made by the carpenter, it’s pretty easy to unlock, since I generally have my carpenter working all the time.
When some of the abilities or roles transfer, it makes sense thematically, IMO (herbalist → cleric, farmer → cook). But I agree it’s not the prettiest solution. I’d love to see trappers upgrade-able to a cook-type job, but that would take some revamping of the class system entirely. I know Radiant was working on redesigning classes (and their abilities), but I haven’t heard much since.
Last I remember, they showed off a prototype involving exploring to unlock new classes, made it clear that it was just a prototype and not a definitive direction, got loud complaints about the direction of the game anyway, put even more prototype disclaimers on their next video, and then moved that all behind the scenes as the new building editor and recently revealed multiplayer took the focus.
That was… not a particularly good time in the DIscourse. Or the video comment sections. So I’m worried they’ll try to avoid changing some things entirely when maybe they should be pushing forward on that (but dealing with the fallout more appropriately.)