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I will discuss the exciting perspectives related to the near future observations of supermassive black holes at mm/sub-mm wavelengths. Event Horizon Telescope (EHT) is delivering images of subsequent AGN sources, while continuously expanding its capabilities, adding new facilities such as the Greenland Telescope, and testing observations at 345 GHz frequency. These observations correspond to the most central part of AGN sources we were ever able to resolve, opening tantalizing possibilities to study the region of jet formation, collimation, and acceleration and advancing our understanding of the physics of these extreme systems. Some fundamental questions to answer are related to the role of magnetic fields and general relativistic effects around a spinning black hole, location of the jet acceleration zone and its relation to the high energy emission. There is a lot to learn from observations of individual sources such as M87, Centaurus A, 3C 84, or 3C 279, but it is also extremely interesting to study a population of sources imaged at mm wavelength for the first time. In particular, our Galactic Center black hole Sagittarius A* is an uniquely interesting mm/sub-mm source, in which horizon-scale dynamics of a low accretion rate system can be studied. This is very exciting in the context of the source flaring, which we are trying to understand in a theoretical framework of the quasiperiodic flux eruptions expected for magnetically dominated accretion systems. Near future time domain analysis of a collection of mm/sub-mm light curves of Sagittarius A*, along with new coordinated multiwavelength observations, and perhaps even resolved (both in space and in time) observations of the EHT will necessarily shed light on the physical mechanism behind flares and high energy emission, as well as on the importance of magnetic fields in the systems similar to Sagittarius A*.