I don't think more tank classes will really solve the issues. Right now tanking is just not that involved and people who usually play DPS don't find it as fun to play. So if you add more tanking classes you are just going to get the same tank players playing the new tank class. What needs to happen is tanking needs to become more fun and there needs to be a reason for high level tanks to do low level content. Duty Roulette was a great start but the rewards are meager at best, extra GC seals, not really an incentive right now. If they unlock the GC rank restrictions and introduce a new reason to get seals and add additional bonuses (not just a mount) you might get some more tanks running low level content. Right now I run low level Tam-Tara to get diremite webs but that is only because I am leveling weaver. As it stands the only other real reason to run them is to help people out and maybe as a reward get a commendation.