User brenj at GBATemp has released and consistently updated an IRC client for the WiiU. It currently only connects to freenode, but he has been making revisions to it on a regular basis so perhaps more options will come in the future. It also uses an attached USB keyboard so no gamepad keyboard it seems.
the steps for using are pretty straight forward
Steps to connect:
1. Choose your keyboard layout: (1) US, (2) UK, (3) JAP (4) DANISH (5) FR (6) GER (7) ITA (8) DUTCH (9) POR (0) SPA (F1) RUS
2. Enter your username
3. Enter your password
4. Enter the channel to connect to
It’s a neat piece of homebrew software, some people like to use their consoles for IRC chat I have come to learn and those online clients can be kind of whack.