The format of itemString has changed some in Warlords of Draenor, and I'm currently trying to find out what each number corresponds to.
For newer items added in Warlords of Draenor, it looks like this:
item:116116:0:0:0:0:0:0:0:0:0:0
Stuff like enchantId and jewelId remain, others I do not know, especially the last three nulls.
Older stuff, for example items from Siege of Orgrimmar, have twelve instead of ten zero values. A Mythic Warforged fully upgraded (6/6) version of Xal'atoh, Desecrated Image of Gorehowl would have the following itemString (507 is upgradeId):
item:105644:0:0:0:0:0:0:0:0:507:0:0:0
Nothing special about that. If you however modify the three last zero values to 1, and add some enchants, you get the following:
The last three zero values seem to be modifiable in a range of 0-3 with seemingly different results depending on item designation. Applying X:X:X at the end of itemString of an item from Warlords of Draenor, with an itemString featuring twelve zeroes, returned entirely different results.
itemString has always been kinda wonky, but this seems a bit overboard. It was even possible to have the item display as a Pristine Crafting Material.