UPDATE: Off-TV Play in Wii Mode, along with USB keyboard support added in the update.
http://www.nintendoworldreport.com/news/35571
UPDATE: The Wii U Firmware update added new enhancements to the system. Wii Games can now be played on the GamePad, though you still need to control the games with Wii Remotes, etc., and Wii games now can output Dolby Pro Logic II. The console will also now be able to automatically download software from Nintendo. Support for USB keyboards was made available and PDF files can be viewed using the web browser. There were also some minor changes including the use of headsets in Wii U Chat, among other small updates.
The rumored system update for the Wii U is now live and available for download. Estimates on the download size are placing it over the 600 megabyte mark.
The update arrives the night before a Nintendo Direct presentation scheduled for tomorrow morning at 10am ET / 7pm PT.
We are currently downloading the update ourselves and will keep you posted with additional details as our downloads finish, and we discover what is within the update.