Yesssss... I also thought about different schools dragons... Classical fire dragon, ice dragon, etc. But... oh... a skeleton/zombie dragon (linked to Dark School) would be like WOA!!!!!
I was actually thinking they would be modeled after Adramelech and have two schools. The fire dragon could be level 4 arcane and level 2 fire. They could also make legendary dragons like that and have lesser dragons that just have the elemental school.
They could do more than one linked to the dark school. There is the skeletal/zombie dragon, they could do a dark/earth school dragon that lives in the depths of the earth.
We can't forget the forest dragon linked to the nature school and the celestial dragon linked to the holy school.
There are so many dragon possibilities they could make a dragon themed or sub-themed expansion.
Here's a thought how about a mage that is a dragon.