As far as I can tell, Software Defined Networking (which this is about: "P4 is a domain-specific language for network devices") by now is pretty much a decade-old promise that never materialized. I'd still love to be wrong though!

So, let's take the next paragraph: "Before P4, vendors had total control over the functionality supported in the network (...) controlled the rollout of new features (e.g., VXLAN), and rollouts took years"

Anyone has a pointer to any actually available hardware capable of L2 and L3 packet processing where I could have implemented VXLAN in, say, weeks using P4? Again, as far as I can tell, it's all either killed-off-a-long-time-ago, "contact us" vaporware, or exotic 40/100-Gb-only Top-o-Rack gear, and even for those, there is nary an "add to cart" button in sight...