You can load games off of USB HDD right now.
All you need is to get an SD to USB connection adaptor. It costs about 40-50 bones shipped, you can then plug your SD adaptor into your Wii U then connect your USB HDD to your adaptor. You get extra storage, but you are still limited to SD speeds.
Full USB support can take another year or 4 years or forever. There is no answer "SOON" can be tomorrow can be 10 years later.
Remember full CFW was supposed to be SOON on the Vita, but it will mostly likely never happen. Also full CFW (a9lh) just came to be on 3DS, and that scene has been going on for ages. SOON is tantamount to never in any scene.