For the longest time, Nintendo's been rather stingy when it comes to redownloading games from its online eShop from one game system to another, though it's loosened up a little bit when it comes to the 3DS, enabling you to transfer games from one system to another – in case you were upgrading to the new 3DS XL or something. But an interesting new feature has emerged with the Wii U, one that could allow you to download someone else's games if you bought it used.
A NeoGAF member has reported that second-hand console buyers are able to redownload any games that were purchased through the previous owner, even if they've managed to delete their account and personal information from the machine (which, by the way, is usually a recommended action). This ties in with Nintendo's previous confirmation that all user accounts on a single Wii U system could access content without limitation, though transferring it to another system is a completely different matter.
Nintendo hasn't made any comments on the transfer situation yet, but, really, it makes sense. And hey, if you can find a used Wii U for cheap, more power to you!