In a pleasant change of pace, extended maintenance for a group of realms is currently not expected to be further extended today. The following realms, which are receiving hardware upgrades, are expected to be up and playable by 1 PM PDT, as originally promised:
Area 52, Auchindoun, Azuremyst, Blade's Edge, Blood Furnace, Coilfang, Dawnbringer, Exodar, Fizzcrank, Galakrond, Ghostlands, Grizzly Hills, Shattered Halls, Terokkar, The Scryers, The Underbog, Velen, Zangarmarsh
All other realms should be up "in about the next hour," slightly later than the 11 AM PDT goal time.
And now the bad news. There are also some issues with Battle.net account authentication, as is so often the case. Blizzard is aware of the Battle.net issues, and promises to provide further updates by noon PDT.
Update: Further updates on the Battle.net issue will be released at 1:00 p.m. PDT. Most (if not all) Battle.net accounts are unable to log into the game.