***Update***
Maintenance is complete! You should now be able to log in to Destiny with no problem.
***Original***
As expected (seriously, I did say this would happen), today's maintenance on Destiny has been extended. Originally expected to be completed around noon Pacific, Bungie announced just now that they're "still paving the way for future updates behind the scenes."
It's (slightly after) High Noon Pacific time. We're still paving the way for future updates behind the scenes. Stand by. More updates soon.
— Bungie (@Bungie) November 13, 2014
Though the developer did warn maintenance could extend beyond the estimated time, they gave no new estimate for when we can expect the maintenance to complete and service to resume. So for now, Destiny's servers remain down.
While we're not exactly sure what's going on behind the scenes, today's update is focused on preparing the game for "the arrival of a series of updates planned for the next few weeks." This could also include "The Dark Below" expansion, which is set to arrive on December 9, and the improvements to the Iron Banner.
"We know you’re anxiously waiting for all the good stuff we promised. This is the beginning of that work," Bungie said earlier. We'll update you once the maintenance is complete and the servers are back up.