Especially with the current free to play scheme, giving players more reaons to want to try and keep playing a Dragon makes sense.
Bipeds have 28 adventurer and 19 crafting schools. There's a huge amount of variety in terms of gameplay and potentially years worth of grinding.
Personally I love Dragons. They, and their lairs, look amazing. But combat is a bit one dimensional and for most fights success equals executing gold rage whenever it's off cooldown. Because all Dragons are practically identical and bipeds can't fly, most Dragon group combat is a bunch of Dragons piling in on the target and gold-raging it into oblivion.
Putting the notion of extra Dragon Adventurer schools aside, I think there is a very simple way to offer more variety.
Extreme buffs + caster equivalent of gold rage.
Dragon Adventurer is a hybrid class but currently skewed very much towards melee because of gold rage. I've heard a caster equivalent of gold rage is currently being tested? I hope that rumour is true.
What do I mean by extreme buffs? Basically grown-up / ancient versions of Determination and Primal Roar.
Rank V Determination = +180 strength, +162 attack skill.
Rank V Primal Roar = +155 to +205 Power, + 161 spell attack skill.
I propose a series of Ancient Fortitude, Ancient Mysticism and Ancient Benevolence buffs which would effectively allow Dragons to specialise their roles in combat.
Because Dragons are already very capable in the melee DPS department, piling on more power could create balance issues so Ancient Fortitude would be more of a tanking buff. It could offer +armour and + health.
Ancient Mysticism would obviously be for spellcasters, offering more power and spell attack skill than Primal Roar (enough to make spellcasting viable) but also debuffing strength, attack skill and maybe also armour and health.
Ancient Benevolence would allow for a healer / buffer role. It could debuff strength, attack skill, power and spell attack skill and buff primal (for healing power) and possiby allow the use of some new buffs/heals which only work when Ancient Benevolence is active.
Notes
1. To keep these in line with biped multi-classing and how they need to visit trainers to switch, the Ancient buffs might require Dragons to visit a particular location/trainer or be on very long cooldown timers which don't allow rapid switching.
2. The Ancient buffs would need to be marked as undispellable.
3. As per Determination and Primal Roar, these buffs would all need to be incompatible with each other (i.e. can only activate one at a time).
4. These would be quested abilities and could come either as a single buff each or a series of progressively more powerful versions, eg. Ancient Fortitude I through V.
5. In exactly the same manner that additional dragon adventurer schools wouldn't need to change the existing dragon adventurer school, these ancient buffs would in no way change existing dragon gameplay for those who enjoy it. They could keep playing their dragons exactly as they do now.