Even the Wii Shop is closing for a few hours. UPDATED October 16.
Nintendo has scheduled a full online maintenance for Monday North America time that will take all of the services offline for a few hours.
The maintenance is scheduled to take place from 1 p.m. Pacific (4 Eastern) to 5 p.m. Pacific (8 Eastern) on Monday, and will affect all of Nintendo's online services down to the DSi and Wii shops. During this time, all games will be restricted to offline functions and the eShop on both consoles will be unavailable.
Traditionally, these cross-console maintenance periods have resulted in firmware updates for the 3DS and Wii U. We will be monitoring the situation Monday to see if anything major - such as the DeNA-developed loyalty program - emerges from it.
UPDATE: The maintenance schedule has been changed: Online play and leaderboards will be down from 2 Pacific/5 Eastern to 7 Pacific/10 Eastern, while the shops and "using Nintendo Network ID" will be down at the old times.