Can we design a coaxial rotorcraft without tail and tail boom completely? What might be the consequences?
The horizontal tail surface is there to generate downforce that holds the nose up in cruise. Without it, the faster you go, the more the nose points down as the machine's body wants to "trail" so to speak behind the tilted rotor disc.
The vertical tails are to provide a weathervaning effect to make the machine passively point ahead in forward flight without requiring a torque control input.
Take those surfaces away, and you are stuck with pointing down at an unpleasant angle while cruising, and having to constantly work the pedals to keep it pointed straight. A fly by wire yaw stabilization system working the pedals in the background could probably take care of the yaw part, but I don't know how you could deal with the pitch part without a stabilizer surface.