Nintendo promised it'd bring faster Wii U menu loading in a system update, and it certainly seems it'll deliver. The company has released a video showing the main menu loading a good fifteen seconds faster after quitting a game under the upcoming firmware--a whopping 60% improvement.
The spring update, arriving in April, is only Nintendo's first step towards improving loading times. The summer update is also due to help, though how and by how much is a secret for now.
Here's the demonstration (via Siliconera):