Server maintenance for patch 3.12 has been announced for 10/1! At 3:00 AM PST for NA, 05:00 UK Time for EUW,and 03:00 CEST for EUNE, servers will come down for an update.
Here's Riot Evo's announcement from the NA forums:
On 10/1/13, starting at 01:30 AM PST, ranked queues will be disabled in preparation for patch 3.12. At 03:00 AM PST, the servers will be shut down and all games currently in progress will end in a draw and stats will not be recorded. We estimate the battlegrounds will be unavailable for 6 hours."
While we never know exactly what will be in a patch until the patch notes go up, the current cycle PBE would lead us to believe 3.12 will contain Olaf's kit update, Championship Thresh, new permanent ward skins, Garen's visual update, Creator Viktor, and more.