They would win me over right there and then if they bought SEGA and all future SEGA games were exclusive to Nintendo. Adding to that the announcement of Sonic Adventure 3 and the unveil of the new HD Zelda.
On the 3DS front i could use a new zelda aswell and/or a new golden Sun and Pokemon in 3D. Not really in Nintendo's hands, but a new Grandia/suikoden/Chrono/Lunar would get me very excited for owning a 3DS.
This would be more to blow me away with excitment. But just a SEGA buy would do wonders for the Wii U in my opinion. It would add the more hardcore gamer to the system without risking the Nintendo brand.