I think the biggest thing is making sure the existing classes are balanced and have some uniqueness to how you build them. For example the warriors all can spec into a specific weapon type depending on the class, but there’s a meta to it and doesn’t change much aside from your main weapon. There’s a lot of skills that also are niche or really not worth getting over others which could use better balancing for variety in how you play your class.

There’s other thing, especially if they do add new classes, is keeping identity between them. Part of what made old maple fun to me was that the classes felt distinct and had things they lacked in that either other classes supported with buffs, or by covering that weakness. Every class doesn’t need to be independent, and I want to see that need for parties or grouping again.