If an update is available for the Wii U, the Wii Mode will be disabled until the update is done.
As of the 7th December 2012, HBC can be installed within Wii Mode on the Wii U using the latest version of the HackMii Installer: http://hackmii.com/2012/12/hbc-release-for-a-new-wii-u/
As of June 10th 2013, Riivolution now works in wiimode on the Wii U. To run Riivolution, you can install it through the HBC by downloading the HBC first from http://please.hackmii.com, or through smashstack by downloading the .elf file from http://rvlution.net/riivolution.zip, extract the contents and place the boot.elf in the "apps" folder on the SD card, or leave boot.elf in the root of the SD card and run through smashstack.
The following list of exploits work in the Wii U's Wii Mode. These exploits all require a particular original Wii game to be inserted. All other publicly-released Wii exploits (such as Twilight Hack, Bannerbomb, LetterBomb) do not work in the Wii U's Wii Mode. The games used in these exploits do not support SDHC cards - use a 2GB SD card.
|Exploit name||Game required||USA||JPN||EUR||KOR||Notes|
|Eri HaKawai||Tales of Symphonia: Dawn of the New World||Yes||Yes||Yes||No|
|Indiana Pwns||LEGO Indiana Jones||Yes||Yes||Yes||No|
|Return of the Jodi||LEGO Star Wars||Yes||Yes||Yes||No|
|Smash Stack||Super Smash Bros. Brawl||Yes||Yes||Yes||Yes|
|Yu-Gi-OWNED!||Yu-Gi-Oh 5D's Wheelie Breakers||Yes||Yes||Yes||No|| SCART cable users: You must connect a SCART lead and use the save 50Hertz + configure output 576i for France
HDMI users: Make sure to use the 60hz version of the exploit