SEGA appears to have another game project in the works, as a new teaser site has been opened up. Other than for the site url (http://miku.sega.jp/mmr/), the only other info we have for now is the opening date for the website: April 18th.
The teaser page can be found here. And according to SEGA’s twitter post, there will also be an update in the weekly Famitsu magazine. Anyone care to take a guess at what it could be, and what “mmr” could possibly stand for?
[Updated 4/16/2013] I previously guessed it was a second Project Mirai game for the 3DS, and it looks like the Weekly Famitsu has confirmed this (via TaleTaleSource).
初音ミクProject mirai2（仮題） (Working Title)
発売日／2013年秋発売予定 (Fall 2013 Release)
リズムゲームは全曲タッチモードとボタンモードがある。収録曲は全てフルサイズで収録される。(The game will be playable in both touch screen and button press modes. All songs used will be full-length)
Images by Japan Otaku Channel.