I don't see why it won't eventually outsell the GameCube. It has a much longer way to go in regards to price.
GameCube launched in the UK at £129.99 and dropped to £99.99. It really never had anywhere to go.
Wii U launched at £299.99 and is currently £249.99. Mainstream prices for consoles here are £199.99 (for cutting edge ones). I do think when Nintendo can get to the sub £149.99 mark they will be able to find a much broader userbase. Especially as more of their big name games will be out.
With the likes of Mario Kart etc on the market too, I do think they might be able to convince a few more Wii owners to upgrade as well. My estimate for Wii U is about 30-35m lifetime based on what we currently know and likely predictable future events (such as price drops).
RIP Dad 25/11/51 - 13/12/13. You will be missed but never forgotten.
