It’s a possibility they left out hidden class files as well, anticipating people looking through them. I figure sometime the level cap will raise and we’ll have more classes that are normal and maybe anything rank 7 and above can have a hidden class but may not always have to be that way. I have a feeling that so far only Appraiser, Puppeteer, and Plague Doctor are the only hidden classes and those other ones we don’t see yet are only rank 7 and will be obtainable by everyone once the rank limit is lifted.
Personally the idea of hidden classes seems okay as long as they aren’t actually going to limit them, because in the end everyone will figure it out no matter how hard it is to find. As people have pointed out earlier, making limitations on the number of people that can have that class isn’t good if those players were later to leave the game. The only solution I can think of is that hidden classes shouldn’t count as an actual rank class but rather an extra set of skills you obtain from the npc, that will disappear if you don’t talk to the npc after a certain time period like 1-3 months? That way when there is a cap on the class it isn’t locked away forever because someone left. The only downside to that is, I’m sure there will be people who purposefully log in just to block people from getting that, even if they don’t play the game themselves anymore.
As for making the hidden classes a random encounter… I don’t think people will like such luck based events. But my feeling is that finding the hidden classes is more going to be a matter of how your build is shaped very specifically, so if you do discover it, by the time you try to reroll it might already be full. Making it random though, my worry is that no one will find it, at all. There’s also issues with the hidden classes could possibly be unbalanced in some way but because so little people play them it won’t be clear how. It would be truly awful if they were OP, because then it wouldn’t be about skill or figuring out a build but solely just luck.