Methods and apparatus are described for adding one or more features (e.g., high bandwidth memory (HBM)) to a qualified stacked silicon interconnect (SSI) technology programmable integrated circuit (IC) region by providing an interface (e.g., an HBM buffer region implemented with a hierarchical switch network) between the added feature device and the programmable IC region. One example apparatus generally includes a programmable IC region and an interface region configured to couple the programmable IC region to at least one fixed feature die via a first plurality of ports associated with the at least one fixed feature die and a second plurality of ports associated with the programmable IC region. The interface region is configured as a switch network between the first plurality of ports and the second plurality of ports, and the switch network includes a plurality of full crossbar switch networks.