Lol your idea is boring and dumb allowing anyone to be anything is not so great Monk use hand to hand how would you be a conj and call yourself a monk using a staff? that make no sense.
The two system i was thinking was
Like FFXI unlock any job with any class and and they have there own Wep
Or
Pug level to 30 unlock Monk
Your now level 1 monk with it's own JA,WS,Spell
but i guess SE are to lazy and don't have time to make such a system like that and they did it the lazy way.