Diablo II ladder reset has been announced for May 17, 2016 at 10:00am PDT. This maintenance will also include a Diablo II patch from 1.14b to 1.14c that addresses a few bugs from the previous 1.14a and 1.14b patches.
The full announcement can be found on Blizzard's forums.
Update 2016-05-17 5:52pm: Blizzard has taken the servers down as of 12:00pm CDT and as of now they are still down while they perform maintenance. More information can be found in their new forum post. Thanks all!
Update 2016-05-17 9:48pm: All maintenance has been complete and the servers are all back online!