From what we see, the Taken seems to be the last in line of all the types of eneny that could appear in the world of destiny. The next couple dlcs will evolve around current enemy types such as cabal and fallen. I personally feel a bit disappointed if all we will be seeing in the future are enemies such as 10 metres tall cabal generals with few changes in armor or a supersized shank with sidekick shanks (-_-). The universe is limitless (we will discuss that later) and i am sure we can come up with many more enemies in different variants.