Next month's big 3DS system update comes with a few cool new features, including YouTube, the Wii U's Miiverse, and a balance combining service that will (finally) let you combine your 3DS funds with your Wii U funds on one unified Nintendo account.
When the update goes live, all you have to do is sign up for the same username on both systems, and you'll be able to merge your 3DS funds with your Wii U funds to buy games on either platform.
Nintendo announced the news during their Nintendo Direct this morning. Still no word on whether they ever plan on implementing a system for recovering your digital games if you lose your 3DS.