Found this potential image of the upcoming Nerf Super Soaker DartFire on this website in Germany. Looks like it will feature some sort of pressurization (it has a trigger), but appears to be a water blaster/dart gun hybrid. My current guess is that it will fire darts together with a stream similarly to how the Nerf Super Soaker Tidal Torpedo Bow shoots water and/or foam rockets.
That said, I don’t have high expectations in terms of its performance.