Solid oxide fuel cells (SOFCs) and electrolysis cells (SOECs) are promising energy conversion devices, on whose basis green hydrogen energy technologies can be developed to support the transition to a carbon-free future. As compared with oxygen-conducting cells, the operational temperatures of protonic ceramic fuel cells (PCFCs) and electrolysis cells (PCECs) can be reduced by several hundreds of degrees (down to low- and intermediate-temperature ranges of 400–700 °C) while maintaining high performance and efficiency. This is due to the distinctive characteristics of charge carriers for proton-conducting electrolytes. However, despite achieving outstanding lab-scale performance, the prospects for industrial scaling of PCFCs and PCECs remain hazy, at least in the near future, in contrast to commercially available SOFCs and SOECs. In this review, we reveal the reasons for the delayed technological development, which need to be addressed in order to transfer fundamental findings into industrial processes. Possible solutions to the identified problems are also highlighted.