Another option is to print solid, with 100% infill, then place the part in a tin filled with very fine salt, and bake it to re-melt the plastic to make a solid block w/o layer lines (note that this requires the use of a plastic which will melt and resolidify a second time and be usable).
That said, additional axes beyond XYZ seem to be the next major development for hobby CNC --- looking forward to seeing what folks come up with.