Millimeter-wave (mmWave) band communication is a very promising technology for 5G small cells. In practice, such a new system will coexist with legacy or evolved microwave band systems, such as E-UTRAN LTE macro-cell cellular systems, for a long time to come. Considering the typical scenarios where a macro cell offers umbrella coverage for clusters of small cells, several user plane (U-plane) architectural choices of macro-assisted 5G mmWave systems from both UE and network's perspectives are evaluated. The proposed On-demand Reconfiguration U-Plane Architecture (ORUA) for Macro-assisted Millimeter Wave (mmWave) small cells is designed to meet 5G expectations of dense deployment of small cells and UEs and beamformed intermittent Gbps links.