Linux Kernel Eyes IPv6-Only Builds, Legacy IPv4

This is half April Fools, half legitimate kernel housekeeping: the joke is the naming, but the architectural direction makes sense for a codebase that still carries a lot of shared IPv4/IPv6 baggage. Splitting protocol support at build time could simplify kernel maintenance and trim dead paths in environments that only need one stack. IPv6-only builds are most useful for appliances, embedded systems, and controlled infra where unused networking surface is a liability. The "Legacy IP" framing is provocative, but any real deprecation would need a long runway because the ecosystem still depends on IPv4 everywhere. This fits a broader Linux networking trend toward making core stacks less modular and easier to reason about at build time.