Yes, ion thrusters still use conservation of momentum to generate thrust. They aren't limited by how fast or how hot we can make something explode though, so we can shove way more energy into the stuff they're throwing out the back. They're basically tiny coil/railguns, using electricity to move individual ions really fast.

In terms of efficiency, Ion thrusters are 4 to 40 times better than liquid fueled rockets. The draw back is that ion engines make very little thrust for the mass of the engine.

Yes, just like every new electrical generation method is steam, every new method of propulsion in space is throw something at the back as fast as we can.

The exception being Project Orion. The idea behind project Orion is to constantly drop and explode nuclear bombs behind the spaceship at a rate of 1 bomb per second. The explosion of the bomb would then push the spaceship forward.