The real nightmare scenario is not just finding a vulnerability in the Linux network stack but finding vulnerabilities at the protocol level in TCP/IP itself or HTTP. That’s a problem that cannot be fixed. Has there ever been a precedent for this in computing?
When these things come up, what usually happens is implementations stop following the spec as written.
Many issues can be handled with minimal coordination, but some things work much better with consensus and you see flag day campaigns. Ipv6 flag day had very limited impact on that day, but may restarted the process and actually got things moving. DNS flag days have been successful.