In order to meet the diverse needs of different services and applications in the B5G era, seamless integration of fiber and wireless network segments of next-generation radio access networks (NG-RANs), with flexible/fine channel switching granularity and ultra-low latency, is vital for enabling dynamic and continuous flow of heterogenous signals of various characteristics across different network segments without optical-electrical-optical (O-E-O) conversions or digital signal processing (DSP) at intermediate nodes. To address these requirements cost-effectively, we experimentally demonstrate 3×1.333 Gbps flexible BBU-UE connections over 10 km standard single-mode fiber (SSMF) and adaptable millimeter-wave (mmWave) wireless reach up to 50 m, using free-running laser/envelope detection-based tunable mmWave generation/detection, and soft-ROADM-enabled dynamic sub-wavelength-level channel switching. The proposed technique requires no O-E-O conversions or DSP at intermediate nodes and offers dynamic RRH-controllable mmWave transmission with large frequency tunability and adaptive wireless network coverage.