I believe that SDCC exclusive Darth Vader / Sith Eyes Anakin is the first in this line.
From the latest newsletter:
"The announcement of the Darth Vader (Anakin) - Sith Apprentice Comic-Con Exclusive brings a new category of figures to our Star Wars 12-inch line: The Lords of the Sith! We're very excited to kick off the Sith Lords with Anakin, who changed the Galaxy forever as Darth Vader, ruthlessly acting under the control of the diabolical genius, Emperor Palpatine. Read the following article for more information about the much-anticipated Lords of the Sith, and refer to the Comic-Con section of this newsletter for a first look at Darth Vader (Anakin) - Sith Apprentice!"
Hopefully we'll see another Sith Lords figure announced before Comic-Con, in which case, like you said, I'm sure it will be Darth Maul.