Well, minus the pulse, which would be great for air-breathing engines too.

If you made a ring of pulse-detonation engines that fired one after another in sequence, you'd almost have such a thing. Connect the tubes side-to-side if you can, merging them into a coaxial detonation chamber with a helical detonation wave that rotates. (looking almost like an annular aerospike engine but leaving a helical exhaust trail) You probably need to run with more than one helix in the engine to avoid disastrous vibration.