The Htasune Miku and Future Stars Project Mirai demo Sega announced a couple of weeks back may be seeing release today. An post at the game's official Twitter says that we can probably expect something good today since it's 2/22 (all 2s!). The Twitter post says to check the Nintendo e-Shop tonight.
Of course, tonight is Nintendo's latest Nintendo Direct broadcast. The past two broadcasts have been accompanied by major updates to the e-Shop, including demos and 3D videos. It's likely that the Miku demo will be one of the big surprises Nintendo CEO Satoru Iwata reveals during the broadcast.