  We discuss the potential of future proton decay experiments on the
exploration of the flavour space of grand unification. We focus on an
economical SU(5) grand unified model (GUT) with the fermion sector extended by
including only one copy of 24-plet. Neutrino masses are generated via
type-(I+III) seesaw mechanism with the lightest neutrino massless. Gauge
unification requires masses of fermions in the 24-plet to be hierarchical, in
particular, the electroweak singlet and triplet heavy leptons to be around the
canonical seesaw scale and TeV scale, respectively. We address how extra
parameters in the flavour space which cannot be touched in flavour measurements
can be tested by a multi-channel analysis in future proton decay measurements.
