The idea that DLCs have to be based on continents/regions/biomes seems very stuck in the community. Occasionally you do see other ideas, but it really isn't often, besides from aviary packs and such.
Personally I would like to see Frontier get more creative with the themes, rather than just doing geographical and biome type DLCs. I am unsure how likely they are to do it. It for sure is easier to come up with themes like that and when the bigger part of the community are expecting them, why even bother getting more creative.
The Aquatic pack might show that they are willing to do things differently, but it currently is really hard to predict. They might as well just continue doing packs for every continent, because it is easy.
I hope they continue this way instead of just being locked to a continent. This way we get a mixed bag, a little bit of everything.