> since required fields don't contribute to b/w incompatibility at all, as every real-world protocol has a mandatory required version number that's tied to a direct parsing strategy with strictly defined algebra

At least I know 10 different tech companies with billion dollars revenue which does not suit to your description. This comment makes me wonder if you have any experience of working on real world distributed systems. Oh and I'm pretty sure you did not read Kenton's comment; he already precisely addressed your point:

> This is especially true when it comes to protocols, because in a distributed system, you cannot update both sides of a protocol simultaneously. I have found that type theorists tend to promote "version negotiation" schemes where the two sides agree on one rigid protocol to follow, but this is extremely painful in practice: you end up needing to maintain parallel code paths, leading to ugly and hard-to-test code. Inevitably, developers are pushed towards hacks in order to avoid protocol changes, which makes things worse.

I recommend you to do your homework before making such a strong argument. Reading a 5 mins long comment is not that hard. You can avoid lots of shame by doing so.