According to the Japanese eShop page, the Xenoblade Chronicles X Wii U digital version will take up a hefty 22.7GB of storage space. This means if you purchased the 32GB Wii U system, this game will pretty much fill your Wii U storage space.
Xenoblade Chronicles, the 3DS port of the original Wii version, will also fill 3.6GB of SD card space. So you know that new 4gb microSD card that came with your NEW 3DS, well yeah, it will fill it completely. Further, Xenoblade Chronicles is currently the only game to require the NEW 3DS to play. One game, one SD card.
If you are planning on playing these massive games digitally, each providing dozens of hours of play time, now is a great time to invest in some extra storage space.