  The Horizon Quantum Mechanics is an approach that was previously introduced
in order to analyse the gravitational radius of spherically symmetric systems
and compute the probability that a given quantum state is a black hole. In this
work, we first extend the formalism to general space-times with asymptotic
(ADM) mass and angular momentum. We then apply the extended Horizon Quantum
Mechanics to a harmonic model of rotating corpuscular black holes. We find that
simple configurations of this model naturally suppress the appearance of the
inner horizon and seem to disfavour extremal (macroscopic) geometries.
