I would like this option, to make it easier to run a CI environment truly IPv6-only. As in socket() to create a v4 socket should fail.

seccomp could only do this partially, in that there are other avenues (e.g. io_uring), and I want it to be the case throughout the boot process.

Creating a v4 socket should map to a v6 address lower down, making v6 transparent to v4 only applications.