This goes hand-in-hand with the print-out that we had last week...
This was found by reader Spirit_of_Tidus via email. GameStop sent out an email saying the game was up for preorder, with the Wii U version listed in that as well.
UPDATE 2 - Amazon preorders up as well (thanks Jones!)
UPDATE - Best Buy has added a Wii U SKU as well. Thanks to Jspoon for the heads up!