Even if it is the “best” it gives one target to try to find a weakness in, rather than many.
It sounds as if you’re falling prey to the allure of security through obscurity.
I’d like to remind you of Kerckhoff’s Principle.
a cryptosystem should be secure, even if everything about the system, except the key, is public knowledge
What this is saying is that in a secure cryptosystem all you need to secure is the key.
Curve 25519 is, for the time being, considered a secure cryptosystem. It’s likely that in the future it will become obsolete, but we’re not there yet. When we get there WG will port to a new cipher that is more secure.
Even if you set your configs to not negotiate, just the fact that the stack COULD negotiate opens you up to downgrade attacks. Also, anybody trying to connect would get some kind of hello/response traffic that would broadcast your (non negotiable) configs, so what do you gain from being able to choose, except the ability to make mistakes?
I think your example of SSH is actually the perfect counterpoint to your position!
SSH is versatile but there’s SO many ways to configure it in an insecure way. It’s important for SSH to be versatile because of how many different devices need it, but that also means it’s really easy to have a config that supports crappy ciphers (3DES, RC4, etc), or enabling root login, or pick any other hundred problems that are either due to user misconfigs or just inherent vulnerabilities in a cipher or key exchange method. Its versatility is the core of its weaknesses.
This already happens right now. If you have 22 open, your firewall is getting hammered with bots trying to get in, regardless of what cipher you’re using, trying to exploit known weaknesses.
WG was never meant to be a swiss army knife, even though it is also versatile. It’s designed to be fast, secure, and as dummy proof as possible.
I’m not sure how you’d achieve this. If you have a mechanism to change cipher modes then there would be part of the codebase and handshake that validates settings in some way, which adds potential attack vector.
History shows that every cipher mode eventually will be vulnerable to new computing power, I don’t think that’s avoidable. Quantum computing is the next big event on the horizon, which is why quantum resistant ciphers, even old ones that never really got adopted, are getting a lot of attention if they’re deemed to be quantum resistant.
The important thing is that if, not when, it’s reported that the cipher is vulnerable that people harden their networks in other ways until a new cipher mode is implemented. That’s just how it works IMO. Edge security cannot and should not be your only security method anyways.
Overlay VPNs like tailscale and zerotier are interesting to me because you don’t have to open any ports. I’m sure they have their own inherent vulnerabilities also but they don’t make you punch holes in your firewall, which makes them less vulnerable to random attackers trying to scan your network edge.