We might face an issue of weapons... as someone specializes from lets say Pugilist to Thief he will have to start using different weapon set and kinda start over with leveling the weapon and pretty much a total different way of playing. But still your suggestion is close to be a great solution. Because a mixed class like conjurer can have three talent trees of Black Mage, White Mage and Red mage? But then we have got to another issue that is when a new class gets in action like SMN and BLU, you cant fit it under any of the current classes ... and even if you made it alone yo uhave to also make 3 trees for it like the rest, and I cant see that working for a class like SMN