A friend of mine watched the stream (she's a big Pokemon fan), and she was Japanese fluent enough to pick things up.
"The game's apparently been in the works for something like three years, which explains why it's being released for the DS and not the 3DS or something. The inspiration for combining the two games apparently came in part from the fact that there's 17 elemental types of pokemon, and in the original Nobunaga's Ambition, there's 17 countries to conquer. (As gameplay footage shown a little later in the conference showed, it looks like each country DOES have an elemental theme to it...)"
"Battles aren't necessarily JUST about fighting! The stage demonstrated featured more of a "capture the flag" task, in which the goal was to capture all three flags on the field.
Gameplay is a turned-based strategy game style, done by player turns. That is, each player moves all of his pokemon, then it switches to the next player's turn. Pokemon retain their elemental advantages and disadvantages from the games, though overall the battle system is fairly simple; the game is meant to be playable for people NEW to strategy games, basically. So if you're an old pro looking for a challenge, this probably won't be the best game for you. (Well, unless Koei includes some kind of hard mode....)
Also, the battle system features a "bushou power" that can be used to power up the pokemon on the field; for example increasing how far a pokemon can move in a single turn."