I would break down the various subclasses into "talent trees" and make telent trees accessible to multiple classes. The idea is that you could completely re-create a particular subclass by hyper focusing your talent tree, but you could also do a little mix and match. I am inclined to want to open up all talent trees to all classes but in practice it wouldn't work because a lot of them rely on specific class features (rage, ki, etc).In your original post, you suggested that PF2 might offer a player better opportunities via class feats. How would this be implemented within a 5e chassis?