I’d say it’s played out ... ambiguously. Conservative HTTP unworkable, liberal TLS dangerous. JSON for internal APIs and data succeeded because it’s conservative, XHTML and XML+XSLT on the open web failed for the same reason. Postel’s law is less of a universal principle than it initially seemed to be, sure, but it appears to me that part of the reason for its increasing irrelevance is our moving away from open ecosystems and not deficiencies valid in its original context.
Integer encoding (as opposed to e.g. encoding of opaque binary strings) actually appears to be a bad example to me: various universal binary encoding protocols, self-describing or not, have an astounding number of unsigned and signed integer encodings among them. It’s like inventing a new one is a rite of passage or something.
