Switch IPv6Traffic to on?

dkg discovers in https://bugs.debian.org/851798 that Tor's SocksPort defaults to IPv6traffic 0.

But Tor Browser set it to 1 18 months ago in legacy/trac#16684 (moved).

It looks like Tor 0.2.4.7-alpha, back in 2012, decided to "wait for enough exits to support IPv6" before turning it on.

Has that time arrived?