I like the idea very much and I've been wanting a tree kind of thing for a long time.

However, I don't think we'll ever see one. It's too complicated for this game. Pretty much everything in FFXIV is very simple and you don't have to read any guides etc to make your char build optimal. The only(?) choice is the allocation of attribute points and nowadays there's only one correct answer to that.

I think the simplicity is one of the big selling points of this game: FFXIV is a very easy game to pick up. Trees would add complexity and the devs might not want that.