The Nintendo Wii and DS, two of Nintendo's last generation systems will be ceasing their online features starting on May 20th, 2014. Online stores will remain, but other things such as online play, matchmaking and leaderboards will be shut down. Nintendo posted a statement about this on their Australian site:
"As of May 20th, 2014, the Nintendo Wi-Fi Connection service will be discontinued and it will no longer be possible to use online features of Nintendo DS/DSi and Wii software such as online play, matchmaking and leaderboards. The Wii Shop Channel and Nintendo DSi Shop will not be affected however, and will continue to be accessible after May 20th."
This means that name big games on both platform such as Mario Kart Wii, Mario Kart DS, Super Smash Brothers Brawl, and all of the Pokémon Nintendo DS titles will no longer be supporting online capabilities.
On the other hand the features that will keep on working after May 20th are: Internet Channel, Nintendo DS Browser, Nintendo DSi Browser, Nintendo DSi Shop, Nintendo Wi-Fi Connection Pay & Play, Wii Shop Channel, and YouTube.