Looking at the full list of titles, I think we're guaranteed at least six (6) 20 million sellers. We've already got one of 'em, and we may get another in the next quarter update.
Mario Kart is a lock for 30 million, it may even do it by the end of December. Not only do I think it can pass Mario Kart Wii's totals, but even the original Super Mario Bros. on the NES (40.24), and become the greatest selling Mario game, period.
Hardware Comparison Threads: