Mixing for smooth time-changes of general nilflows

We consider completely irrational nilflows on any nilmanifold of step at least 2. We show that there exists a dense set of smooth time-changes such that any time-change in this class which is not measurably trivial gives rise to a mixing nilflow. This in particular reproves and generalizes to any nilflow (of step at least 2) the main result proved in [3] for the special class of Heisenberg (step 2) nilflows, and later generalized in [58] to a class of nilflows of arbitrary step which are isomorphic to suspensions of higher-dimensional linear toral skew-shifts.