End-to-end network programmability

I've never used any kind of SDN stack, but I'm under the impression that at least if you want hardware support, you're limited by what protocols your hardware supports with traditional switches, even if controlled by OVS or Faucet. Whereas with PISA and P4, you can just write a new parser and load it into your existing switch, and it will work at line speed.

Now, as I said, I'm certainly no expert on any of this, so please correct me if I'm wrong.