The SPring-8 upgrade plan aims at significant improvement of the light source performance by replacing the existing storage ring with a completely new one. The ultimate goal is to achieve extremely small emittance that is equivalent to the diffraction limit of light in the X-ray regime. For the challenging goal, the new ring features a multi-bend lattice with damping wigglers. Up to now, a six-bend lattice has been mainly studied, and key technologies that support the new lattice are under design. The overall review of the upgrade plan, including discussion on critical issues, are reported.