Negative differential drift velocity in wurtzite GaN has been verified experimentally, yet in spite of the wealth of documented theoretical investigations of GaN-based Gunn diodes, not a single such device has yet been demonstrated. The likelihood of realizing GaN-based k-space transfer devices is reassessed in light of recent theoretical modeling. A new physical mechanism is proposed for the generation of dipole instabilities in wurtzite III-nitride materials, entirely unrelated to the Gunn effect. State-of-the art numerical simulation demonstrates the direct generation of millimeter-wave signals exploiting traveling dipole domains in the plane of a polar heterojunction upon which a simple triode structure is superimposed.