In a recent blog post, Mojang's Daniel Kaplan stated that the company plans to remedy the lack of Survival mode, at least partially. He stated that the goal isn't to completely "replicate" the full experience of Minecraft, as many features simply don't "match the touch platform." That said, many familiar features are planned, including animals, enemies and item crafting. Mojang is also "experimenting" with caves, though the implementation still needs work.
And, of course, Mojang hasn't specified when players can expect these features. That's okay though, because our full scale Battlestar Galactica is going to take a while anyway.