I'm really excited to see this come through. I've never liked aoe2's water play, and part of that is because of the lack of a clear counter triangle that's created because of the fact that demo ships are supposed to be the counter for fire ships. Taking an approach more similar to Age of Mythology (with its arrow ship > hammer ship > siege ship triangle) with demos sitting outside that should make for much more dynamic fights.
And speaking of Age of Mythology, the new boarding ships apparently have a snare mechanic! Which is new to aoe2, but aom and aoe3 have always had it for melee land combat.