I've not seen or heard any sign of anything Freeguild, Devoted of Sigmar, Collegiate Arcane or Ironweld Arsenal coming any time soon. Trust me, if I had, Id be posting it on this forum, where there are a lot of people eager to know anything.
Of the stuff I've heard or read about, they are talking about Deep shadow Cthulu Aelf Sky Pirates, Skaven Clan Skryre Sky Pirates, Grot (Goblin) Sky Pirates.
To be honest, I think some of that stuff is just made up, there seems to be a lot of expectation on another Sky Pirates, but not any consensus on which faction is going to be the real rival for the Kharadron Overlords. It could all be wrong, I'm not putting a lot of faith in any of these rumours at the moment, other than some for of Skaven coming this year.
As for human factions, this is my speculation, we're likely to see the odd model for a quest side game, or a gang for Warhammer Underworlds: Shadespyre before we see a battletome or faction release for the main Warhammer Age of Sigmar game.