TBH i would hate to see hero's on current dragons,would be hell trying to kill that combo.
But mounts in general,would be nice.
I was actually thinking having hero's "attach" to a sqaud,providing passive bonus's to the sqaud,and taking on the sqauds attributes.Meh hate to say this,but warhammerish.
So if i wanted an archer hero,would attach him to archers,the entire sqaud would get some bonus,as elite gaurds or something.Or a knight,or a mounted knight.
I can see dragons being single units,even ogres and treants.But the hero's currently feel out of place with one unit.He needs some freinds.