Riding dragons is still a decent idea for a neutral unit; it's a shame that turning them into bosses results in losing many ideas for new units. And Morning was talking about riders on Ents! So, an elf would be sitting in the crown of a living tree? I understand that you said it as a joke, but some people take it too seriously. And the idea itself is just absurd. Ents are already quite capable units, and they don't need a rider any more than a dryad needs a tail!
It depends on the game. For Heroes of Might and Magic, it's silly, but for strategy games like Warcraft, Lord of the Rings: The Battle for Middle-earth, etc., it's quite interesting.
