ESRB. Although this may give the impression that it'll involve in-your-face Breakout-style action, the rating could very well be for the 3DS's Virtual Console. In that case, it'll be pretty rudimentary paddle bouncing 2D action.
Our theory as to why this isn't an update, but rather a Virtual Console download: "3D" is missing from the title. If Nintendo was going to make a 3D version of the game, it would simply add the telltale two-letter descriptor to the end of the title, right?