Hello,
We still have a depressingly low number of relays that support IPv6 (currently only ~120 of ~1900 relays). If your host supports IPv6, please enable it, especially if you run an exit! This has to be done explicitly.
If you (supposedly) care so much, then can you please make it automatic?
There is no need to explicitly put the ____IPv4____ address into the torrc.
And there is no need to explicitly put the IPv6 address into the config file of virtually any other IPv4+IPv6 supporting software I can think of: web, mail, NTP, XMPP servers, those are all capable of automatically figuring out which IPs the host has.
Can't think of any reason of why this has to be otherwise in Tor, aside from perhaps a certain lack of understanding of best IPv6 implementation practices from the Tor developers side and/or nobody simply giving much thought to this yet.
I currently run 15 Tor relays, 14 of those IIRC are IPv6 capable. But since you did not bother to make enabling IPv6 in Tor anywhere near user-friendly [1], I am simply not going to bother pecking the IPs into each torrc individually. [ One of the practical reasons being that I sometimes need to migrate the Tor 'identity' (torrc + /var/lib/tor/*) between machines and providers with v4/v6 addresses obviously changing. ]
Aside from migrations between providers, the requirement to specify the IP is also impractical in many other situations, e.g. my ISP at home provides only a __dynamic__ IPv6 subnet which changes to a different one with each new PPPoE session.
[1] Ideally there should be no 'enabling' at all!!! IPv6 should be active by default, IF the relay has determined it is able to make a successful IPv6 connection with a dir-authority -- oh and also that's how you can discover the actual working IPv6 address to use; or at least with a simple "IPv6Relay 1, but certainly with no requirement of specifying the IP address in the config file.