The new accelerator complex Nuclotron-based Ion Collider fAcility (NICA) is now under development and construction at JINR. Existing Alvarez-type DTL linac LU-20 now operates as injector of light ions, polarized protons and deuterons to Nuclotron for LHEP experimental program. It provides proton beam of 20 MeV energy and light ions of 5 MeV/u energy. In 2015 the cascade transformer 800 kV which is pre-accelerator of LU-20 had been replaced by the new RFQ linac. The proposal on Alvarez linac LU-20 upgrade by a superconducting light ion linac with energy up to 50 MeV is discussed in this report.