Source:
http://us.battle.net/overwatch/en/blog/19981654/overwatch-closed-beta-going-on-break-december-10-12-3-2015
and also:
Q. Will any more players be added to the Closed Beta before it’s brought offline on December 10? A. No. We have no plans to add any more players to the Closed Beta before it's brought offline on December 10.
:/
My sentiments exactly.
Why would they shut it down over the Christmas/holiday season? That seems like the best time to test since all students are on break.
I suppose Blizzard does deserve a break as well...