Why wouldn't the NFL want to keep it exclusive? I think that unless another company managed to convince the NFL that they would do a good job for the NFL brand and make the NFL a lot of money, then EA will be able to keep it exclusive.
Easy, EA will not drop Madden just because they don't have the Exclusive deal anymore. They will continue to make the NFL a lot of money because, they still have to license the IP from the NFL. This allows the NFL to have more leverage over EA and to fill the gaps in its IP. If EA not producing for the Wii U then someelse could.