  Reconfigurable intelligent surface (RIS) has been suggested to be a key 6G
feature and was suggested to be considered as a study-item in both 3GPP
Releases 18 and 19. However, in both releases, it has been decided not to
continue with it as a study-item, and to leave it for possible future
specification. In this paper, we present the rationale for such a decision.
Particularly, we demonstrate the practical issues which may affect the
feasibility or usefulness of RIS in cellular networks, and present open
problems to be addressed before RIS can be used in practice. Moreover, we
compare the performance of RIS with network-controlled repeater, the node with
the most similar characteristics to RIS and which has been standardized in 3GPP
Release 18. Finally, different simulations are presented to evaluate the
performance of RIS-assisted networks.
