[en] Nuclear g factors are of the most accurate probes in modern nuclear physics investigations. Sensitive to the precise structure of the nuclear states, single-particle or collective nature is accessed directly by their measurement. At the border of nuclear existence, key regions of nuclei both neutron-rich and proton-rich are foreseen for studies. The investigations will cover shell structure, magicity, nucleon-nucleon interaction, collectivity, deformation, and shapes. With the new gSPEC project at the GSI/FAIR facility, such investigations are intended to scan various excited states of nuclei along the entire nuclear chart. Currently, the design of a new dedicated experimental apparatus is being performed, including magnetic system and detector R&D, together with feasibility studies of various scientific cases.