continental drift wouldn't be impossible.
computations themselves don't take a large amount of memory, the memory is just required to store the representation of the continental plates or whatever is being simulated. as with climate, where you can have a zero-dimensional model, one-dimensional model, or even a three-dimensional grid simulation, there are various levels of complexity that can be used to model continental drift. if you went with a very crude representation, the computational effort and memory used would be minimal.
since this seems like a space oriented simulation, i'd be more interested in features like the ability to view in different wavelengths and perhaps view objects like lyman alpha blobs