Does anyone think we should have:

- a water serpent type dragon in the ocean
- a hydra like dragon (many heads etc)
- a earth dragon (one that slithers around underground and jumps out)
- and a bunch of new variants

Some might be hard to implement in the game.

I kinda doubt we are going to see new Dragon-types in Dragonborn, Bethesda already maxed out what they could do with the level 78 legendary dragons.

The new dragons that came with Dawnguard are kind of underwater already. Or was that just for show?

So far, I've only seen in the video one other type and that was the Naz'gul looking dragon in Apocrypha. Perhaps we'll see some other types, but none that you mentioned... Just different skins perhaps. Dragon with tentacles?

What is missing is a dragon whose breath-weapon is lightning.

just a tid-bit; the breath weapons are actually shouts

I'm still waiting for a dragon that just shouts insults at you. Hurtful insults.