There is a general encryption proponent mandate RFC...
One might also try full text RFC search for "fingerprint" references in context of "TLS" (or the older "SSL"). The following incomplete list all in manner of spirit do generally give rise and encourage the offering and enablement of such security option sets in apps / protocols utilizing TLS... Recommendations for Secure Use of Transport Layer Security (TLS) https://tools.ietf.org/html/rfc7525 Pervasive Monitoring Is an Attack https://tools.ietf.org/html/rfc7258 Privacy Considerations for Internet Protocols https://tools.ietf.org/html/rfc6973 Certificate Transparency https://tools.ietf.org/html/rfc6962 Strong Security Requirements for Internet Engineering Task Force Standard Protocols https://tools.ietf.org/html/rfc3365 Guidelines for Writing RFC Text on Security Considerations https://tools.ietf.org/html/rfc3552 IETF Policy on Wiretapping https://tools.ietf.org/html/rfc2804 IAB and IESG Statement on Cryptographic Technology and the Internet https://tools.ietf.org/html/rfc1984 "It is the consensus of the IETF that IETF standard protocols MUST make use of appropriate strong security mechanisms." Privacy Requirements for IETF Protocols https://tools.ietf.org/html/draft-cooper-ietf-privacy-requirements-01 It is the consensus of the IETF that our protocols be designed to avoid privacy violations to the extent possible. Handling Pervasive Monitoring in the IETF (perpass) (WG) https://www.ietf.org/proceedings/88/perpass.html https://www.ietf.org/mailman/listinfo/perpass Not requiring app (NFS) spec implementations to have some options for some of the previously noted modes of fingerprint checking to help avoid some TLS MITM attacks, would seem to be in conflict with all above.