@arlogia that would take so much fucking work, that it would be not worth it for game companies at all.
For freely changing classes FFXIV does it great.
Also the problem in IRL MMO games is that everything revolves around the end-game. Any "new" features or systems where you want to hide how to obtain something, a couple of hours after release there will be a guide online on how to do it. If it's not on par with current skills that are used by raiders it's considered useless. That's why you don't see so many MMOs / MMO-lites released anymore. Metagaming plagued the genre and the social aspects of MMOs were replaced with convince.
Insert Old Man rants at cloud meme here lol