Suggestion: Instanced Battle Relief
This might be a long shot but can you implement a ticket entry system? (Reference point to Ambuscade entry in Final Fantasy XI)
If this continues as is, all people will do is keep stacking on the NPC and spamming. People with the faster connections will be the only ones to get into any instances. Been waiting at this NPC for 19hours...
Alternative possibility:
Consider shutting down all but 1 DATA center for maybe 30min windows (Even just one time around, preferably actually). I know it'd be slightly frustrating but it'd get more people through the gates on every world.