Of course these ideas are not that new. IPv6 was supposed to give end-to-end connectivity to all, and originally IPsec was supposed to be mandatory part of IPv6, giving each internet host cryptographic identity. And so on.
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IPv6 -together with WireGuard- gives privacy, security, and performance. The downside is the complexity to set it up.
Tailscale builds on the shoulder of giants. IPv4, WireGuard, Samy Kamkar NAT punching, OpenSSH, and probably many more. One of the upsides is the combination of these, and that the management interface in general is easy. But what counts for CA is also true for Tailscale: both are using FOSS to in the end deliver a (proprietary) service.
But because almost everything is build on top of FOSS and there's Headscale (and they're cool with it), this isn't a major issue to me. Like, it is a downside, but not a major one, as vendor lock-in is practically non-existent. In fact, it is likely an upside from a business/support PoV.
My laptop has an IPv6 address, as does the router that routes its traffic. There’s no NAT, that’s true, but there’s still a firewall — only inbound packets from a destination host and port that have been sent to are allowed in. And in enterprise environments, from what I’ve seen, there’s a symmetric NAT on IPv6 anyway — packet comes from a different IPv6 address and randomized port than the one client sent it from, making peer connectivity impossible, as the source port varies by destination host and port.