My guess is as good as yours, but as a phoenix wright player, all I know is how Ace attorney series plays, I bet there will be courtroom and pressing parts along a much bigger adventure in which you solve puzzles.
 
HOLD IT!

One more thing, I don't know what about you, But I'm gonna buy it just for the sake of Phoenix.

Puzzles with contradictions, or something like that. I believe that's what they've said.

Witch Trial part(s) will be handled by Phoenix Wright and there will be puzzles with contradictions solved by both characters.  Something like that.

I bet there's going to be two seperate storylines to force you into Layton's perspective, just a hunch. 
His [Layton] sidekick creeps me out.
 
But LEVEL 5 is awesome, they're a classy act, Capcom as of later has been holding games hostage.