We present an overview of the concept of multi-connectivity, as seen from the user-plane perspective of 5G mobile networks. The potential of multi-connectivity is discussed, when utilized towards higher throughput and/or higher reliability in 5G. Two major architecture options are considered, namely the traditional X2-based approach, and an architecture with centralized packet data convergence protocol (PDCP) layer, which are associated with different network deployments. An assessment of multi-connectivity over its intra-site counterpart, carrier aggregation, is presented, in terms of performance potential as well as in terms of the technical challenges involved.