On the one hand we haven't gotten that highly coveted XIV-original job yet (Assuming GNB and AST which were both based off a character or two each, doesn't count), so there is a chance that the devs would make a new healer whole cloth.

OTOH that we're 3 expansions without said job already implies the devs perchance to borrow from older games instead,making Chemist more likely.

BTW why do people want/expect a completely original job anyway?