Good idea, but as previously pointed out, the processor just wouldn't be able to handle it, Plus, the amount of effort that the developer would have to go through in order to get Nintendo to approve it would be tremendous.
Plus you'd have to consider that the language that Universe Sandbox is written in may not be compatible with the DS.
However, a simpler option would be the iPhone/iPod Touch, It sports a 533 MHz processor, compared to the DS' 67MHz. Add 128MB of RAM. And, with a Multitouch screen, you could get maximum control over your universe.
And the really nice bit about the iPhone/iPod Touch, The developers license is only $99, and that entitles you to all of the Developers Software, the ability to test it on the actual device, Full Support, and the ability to publish the content to the Appstore.