[kevin_thibedeau]

> What about IPv6 makes it such a chore to become widespread?

Any code storing an IPv4 address in a uint32_t can be hard to port to IPv6. Likewise, many codebases have their own ad hoc parsers for IPv4 dotted quads and would choke on anything else.

[xxpor]

The additional 12 bytes to store the v6 address might not be trivial to find as well (connection state tables in kernels, additional space in DBs). There's also MTU issues.