There's a five-page spread in the recent Dengeki G's magazine that gives some details about the game.
The gameplay seems much like a normal action RPG (you can customize your equipment, skills, etc.), and they've preserved the sword skills and "switch" mechanic from the original story. From what I can gather, most of the battles will occur in parties of two. You have a certain amount of skill points in your battle turn (to use sword skills), and then you can switch out and the partner takes over while you can only use defensive skills (like parrying, side step, etc.). I assume that your skill points will recharge during this period, and when the other person's skill points run out you'll switch back. And yes, there will be boss fights too.
No date has been announced yet, but I would guess we'll see it in early 2013. I'm not sure if it'll be able to stand on its own as a really great RPG, but it should still be fun for fans of the franchise.