But there's now multipath TCP handover? Weird behaviour to want different network interfaces on different network share the same IP, and pass it along like a volleyball?

Wi-Fi and ethernet also have different IPs. And what if you also add Wi-Fi peer-to-peer (Airdrop-ish), Wi-Fi Tunneled Direct Link Setup (literally Chromecast)?

If a vendor implemented simultaneous Dual Band (DBDC) Wi-Fi, that means it can connect to both 2.4ghz and 5ghz at the same time, each with their own mac & ip, because you're trying to connect to the same network on a different band. Or route packages from a 'wan' Wi-Fi to a 'lan' Wi-Fi (share internet on (BSS) infrastructure Wi-Fi A to a new (IBSS) ad-hoc Wi-Fi network B with your smartphone as the gateway on Android.

There's also 802.11 the IEEE 802.11 standard to add wireless access in vehicular environments (WAVE) and EV chargers or IP over the CCS protocol, etc. If all cars need to be 'connected' and 'have a unique address' NAT / CGNAT also isn't cutting it.

There's also IoT. Thread is ipv6 because it's the alternative to routing whatever between wan / lan / zigbee / Z-Wave / etc with a specific gateway at a remote point in the mesh network.

And how about the new DHCP / DNS specs for ipv6, you can now share encrypted DNS servers, DHCP client-ID, unique OUID, etc etc.

It's an infuriating post really. As if IP was only designed for a small scale VPN / overlay network service such as Tailscale.