A disc reader woukd be too much hassle in the eyes of the consumer. You woukd not be able to use it for portability, so whats the point?
Plus most people who have their WiiU games, still have a WiiU due to rarity. Not enough people would benefit from that to make it worthwhile. Hell I would even go as far to say that even the Wii owners still have their console if they kept their games. WiiU was the only console to upgrade to, and hardly anyone did it.
VC and WiiU remasters, believe it or not, would be far better than this kind of BC. At keast this way there are no extra pieces and all games remain portable. I am sure some of the Wii games would be the exception due to motion controls, but it would still be easier IMO.