At a minimum, a lot of IoT devices that use IPv6 exclusively – eg the Matter standard – can finally stop compiling extra support for Legacy IP that they just don’t use. The kernel savings will likely be modest, but in an era where more and more things are being squeezed into less and less RAM – not necessarily due to DDR5 prices, since microcontroller SRAM is a different animal entirely – this will be appreciated as some breathing room for embedded developers.

There’s also the security argument, where disabling Legacy IP means that the (relatively few) CVEs against the IPv4 network stack simply won’t apply. Reducing one’s attack surface is always a good thing, if simply to reduce the number of warnings from software supply chain scanners.

I’m under no misapprehension that Legacy IP would be switched off as a default in the Linux kernel anytime soon, but offering a real choice means developers can actually customize their kernel build to be as optimal as possible. It removes a technical barrier, meaning all that remains is the political matter: the will to turn off Legacy IP entirely.