I am trying to concurrently direct traffic out through either wifi or cellular within Packet Tunnel Provider

Why is "bind" allowed outside of the tunnel provider, but not within? Does this mean we can't use both Wi-Fi and Cellular simultaneously (like in Multi-path TCP) within the packet tunnel provider. It would be really good to allow "bind" within the tunnel provider in the future iOS release so that we can develop multi-path VPN for iPhone.