This paper describes experiences gained during the development of a Proof-of-Concept implementation of NewIP/BPP, the protocol at the core of a novel packet-programmable networking framework, using P4, a popular SDN technology for the implementation of networking protocols using protocol-independent packet processors. NewIP/BPP introduces a number of novel requirements whose implementation encountered a number of P4 limitations that proved very challenging to overcome. We hope that the resulting insights will be useful for future implementations of NewIP/BPP as well as for its and P4's evolution.