OTOH IO::Socket::INET buys 14 years of backwards compatability:

Don't be so sure. Just because it buys you 14 years of being in core doesn't mean that much. The current version of IO::Socket::IP has full test passes on perls as old as 5.8.1, so you are only buying something like three and a half years of extra backwards compatibility. Contrast that with how much forwards compatibility you would be buying with IO::Socket::IP in terms of transparent IPv6 support.