As for the show, I'm actually thinking if it will have enough mecha. The whole alien race fighting seems like it will be the major factor of the show, and the element the plot would revolve around. But it could also be just backstory, and we could have this be an adventure anime with touches of iyashikei.
Yes, I know it's Urobuchi, and Murata doesn't seem like the type of guy who would do that anyway, but there's a chance. They may never go back to this "space-time warp" and see the aliens again, the whole show could be set on the water planet with any potential threat being an insider.
I don't hope for that, I want fight scenes and hideous aliens. But one can never be sure on this industry...