Interesting stuff. What I'd like to know more about is why did the introduction of sea/land suddenly solve their design problems. The blog-post was kinda vague on that part.
This should be clear: sky combat was previously just a few layers of altitude + nice looking background. No big deal.
Introducing land/naval units means more strategy, as they're limited in their movements. Probably these units will deal greater damage or represent supply chains that play a vital role in combat.
Next, comparing a dragon to land/sea creatures is much more fun than to other flying things (woaw I'm a dragon look at me how fast I fly I'm superior!!!). And now you have the option to crush on ground or sea. Perhaps they'll add functionality to dive under water for a few seconds, that would be nice!
I say the ocean's the limit!
