I think more tank and healer classes would be fine. Make them over powered. Give them some exciting dps traits. Dress them and sell them as dps but with tank and heal abilities (obvious they have to fit in the heal and tank slots in parties). But make the requirements for getting these new classes hard so not everyone and their neighbor can pick them up. Not selective tho. Like I wouldn't say, "requirement you must be in an FC" (solo players screwed) or "you must have your chocobo's fighting tree maxed out" (annoyingly to hard) or "all crafting at level 50" (not everyone's cup of tea). That just seems to invade people's right to do as they please with what's been given. So I'd make requirements something new never yet done.