A "new" Seiken Densetsu (aka Mana) has been revealed for the Playstation Vita and mobile platforms. It's actually a full 3D remake of the original Gameboy game from 1991. Westerners will know the game best as Final Fantasy Adventure, or Mystic Quest.
The game is out this winter in Japan. No word on any localisation, though I wager the mobile version would have more of a chance to come over than the Vita version.
Additionally, NeoGAF's duckroll has this to say:
The Dengeki interview is interesting. I've only had time to skim it a little, but the guy in charge says that they're remaking the first game in 3D to act as a foundation for more remakes in the series. Mainly so they can have all the older titles from SD1-3 on the same platforms in 3D sharing assets and whatnot, and it can pave the way for a SD5 possibly. They're taking into consideration the demands of fans with the coming anniversary next year. They're also planning on releasing this remake on PS4 in future, but they'll only work on that after releasing the portable ones. For a downloadable stand alone title like this, he estimates the price will be about 1400yen. So 10-15 bucks.
If the naming confuses anyone, here's a brief summary:
JP: Final Fantasy Gaiden: Seiken Densetsu
NA: Final Fantasy Adventure
EU: Mystic Quest
The SNES FF spinoff is:
JP: Final Fantasy USA
NA: Final Fantasy Mystic Quest
EU: Mystic Quest Legend
This particular remake is of Seiken Densetsu/FF Adventure, NOT the infamous Final Fantasy Mystic Quest that's the stripped down RPG.