In order to meet higher requirements of 5G loT and emerging vertical fields, 3GPP Rel-17 has studied and formulated relevant standards for UE with reduced of capabilities, i.e., RedCap UE. Different from normal UE, the capabilities of RedCap UE are reduced, which may then cause potential coexistence problems with normal UE, especially when there are multiple types of RedCap UE. In this paper, we provide a comprehensive insight on key characteristics and standardization progress for Rel-17 RedCap UE. To further deal with potential coexistence problems, solutions on early indication and bandwidth part configuration of multiple types of RedCap UE are proposed and analyzed. Moreover, potential evolution on Rel-18 RedCap UE is summarized, aiming to realize a real world of “connected and intelligent, green and energy saving, small and smart”.