(Repost of <https://news.ycombinator.com/item?id=38570370>)
(Repost of <https://news.ycombinator.com/item?id=38570370>)
Even if something is open, complexity is almost like closed as we can see with crazy complicated web standards for which there are few implementations.
A simple protocol is more likely to last.
IPSec is not always a VPN protocol. L2TP over IPSec is often used as one, but IPSec does little more than encrypt a tunnel between two IP addresses. IPSec in tunnel mode can be a minimal VPN, but it's not used as such as in VPN scenarios without a second packet encapsulation protocol, as it lacks authorization beyond key exchange.
As for the risk of ossification: that didn't go away with the current system either. HTTPS over TLS 1.3 looks like a TLS 1.2 session resumption on the wire (in its default configuration) because shitty middleboxes are used often enough that it would impede the protocol.
The "let's remake TCP over UDP" approach QUIC takes has very similar origins. UDP is generally allowed by random firewalls over that network, while other (more suited) protocols for this type of stuff like SCTP are not. The operating system doesn't allow opening raw network sockets without high privileges, so adding a new QUIC protocol at the layer of TCP and UDP to implement them at the right spot in the stack wouldn't be usable for many devices. Same is true for the TCP stack you have to use what the OS provides or get higher privileges to do your own; patching the TCP state machine isn't practical. So, if you want to implement a better version of TCP optimised for web browsing and such, you use UDP, because while technically incorrect, it'll work in most cases and has the least restrictions.
In the context of the network, IPSec is the new protocol here, not the result of ossification.