Well from what we know it is possible to transfer downloadable games from one console to another if there is a need for that (broken WiiU for example), so what other problem would this cause other than being unable to share the games with others?
I don't think that Nintendo wouldn't help you if you wanted to transfer your games to a new WiiU. It would certainly be more tiresome than other consoles but it is doable. Changing a console for a new one without the first one breaking or something ain't that common anyway.
When you sell your WiiU to another person you should just make sure that you also charge extra for the included games. But then again when you sell a console you usually also sell its games with it, so it is not such a big deal.