I don't know the answers to those questions, intgr - I'm not one of the admins of the box, I'm just uploading the videos this year :-)
As the conference is frequently at an Australian University, they usually have a direct link to mirror.linux.org.au which is hosted at the Australian National University on AARNET. There are several other mirrors from there, including mirror.internode.on.net that I know of, within Australian. I'm not sure of the full arrangements, not being in that particular loop. I'd imagine they'd welcome other mirrors though :-)
I'll pass on the information about the IPv6 problem and see if the admins can fix that.