Update: It has been discovered that the terms have had this line used as early as 2014, so this is nothing more than a false alarm.
The newest terms of use for Pokemon Trading Card Game Online has an interesting tidbit that was recently discovered on ResetEra. The terms mention that “certain features in the Service may require you to register certain information”, as well as use “Nintendo hardware/software or Nintendo Network to participate in certain features of the Service”. As of this article’s writing, the game has yet to be ported to any Nintendo hardware. Most of this is speculation, so it is nothing more than a rumor for now. If an official announcement is made, we’ll let you know.
Probably a hint that they planned and scrapped a Wii U port.