  Achieving Bloch oscillations of free carriers under a direct current, a
long-sought-after collective many-body behavior, has been challenging due to
stringent constraints on the band properties. We argue that the flat bands in
moir\'e graphene fulfill the basic requirements for observing Bloch
oscillations, offering an appealing alternative to the stacked quantum wells
used in previous work aiming to access this regime. Bloch-oscillating moir\'e
superlattices emit a comb-like spectrum of incommensurate frequencies, a
property of interest for converting direct currents into high-frequency
currents and developing broad-band amplifiers in THz domain. The oscillations
can be synchronized through coupling to an oscillator mode in a photonic or
plasmonic resonator. Phase-coherent collective oscillations in the resonant
regime provide a realization of current-pumped THz lasing.
