superchunk on 11 April 2013
Software is tied to your NNID.
However, currently your NNID is tied to your console (3DS or WiiU).
Nintendo did state that this won't be the case long term. They said THIS YEAR it will change and accounts will be moveable across hardware. With that, I'd imagine the digital games could move to. The caveat to that is it would only be the same hardware. So 3DS to another 3DS or WiiU to another WiiU. Then looking at how Nintendo handles moves of content, it would likely be a one way move and not allowed on multiple hardware at the same time.
