Wii U does support multiple profile sign-ins

Wii U is a great console. Good design, nice feel, and fun to play. It’s not without faults, though. While Nintendo Network is a vast improvement over Wii’s introverted little world, when compared to Xbox Live or PSN, it’s still lacking.

Despite all the restrictions and slow-loading, one of the greatest concerns was the inability to have two profiles playing one game at the same time. It’s a basic, core feature that has been used over the last eight years. So it's natural to expect the same thing to be possible on Wii U.