While these changes don't confirm anything, it is possible that it is a change to prepare the Mists of Pandaria raid to be the new Timewalking raid. Making Mists of Pandaria the next Timewalking raid would be the perfect opportunity for a new source of the now unobtainable Garrosh Hellscream Heirloom weapons.
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Is Siege of Orgrimmar the Next Timewalking Raid? – Removed Items Returning, Garrosh Heirlooms
With today's PTR build, Blizzard seems to be changing some data entries for Siege of Orgrimmar items, including Heirloom items from Garrosh Hellscream.