Reedy mentioned this in a chat. It seems to be missing from the handbook?
Topic on Talk:Hackathons/Hackathon tips for organizers
Thanks! Added to m:Wikimania_Handbook#Freenode (as linked from Hackathons/Hackathon tips for organizers#Wifi). @Reedy (WMF) please clarify that sentence with details on who to contact etc.
I've further tweaked based on the phab comment, and added a section for "IP Throttle exception", but we still need clarification on where to contact Freenode and Wikimedia.