The integration of private mobile networks (PMN) driven by next generation train networks (NGTNs) require a paradigm for a secure spectrum sharing with mobile network operators (MNOs) to provide privacy driven architecture. For such unprecedented performance expectations, a fine-grained spectrum sharing PMN is required to address secure communication with volume, time, and usage area parameters. In this article, we study a novel vision for empowering secure spectrum sharing for NGTNs with MNOs using blockchain technology by using smart contracts. In particular, blockchain key features and its integration along with the anticipated challenges and potential benefits of the proposed architecture are discussed. Finally, we have also highlighted potential NGTN use-cases to address the outlined challenges. This would unlock several practical scenarios and critical applications to meet rising business demands. From the implementation perspective, this article would exploit a conceptual blockchain-driven intelligent network that is ready to satisfy a number of NGTN applications that need privacy preservation.