So everything below is what I have heard that is in the new season...
1) Yang's theme will return. (Probable to turn Cole human again)
2) Dareth will have a big role. (Replace Jay if he leaves the team)
3) Skylor will be in the season 6 more (cause she was only in one season like the elemental masters)
4) Jay and Nya's relationship will develop (probably cause Jay gets blamed for why they are wanted)
5) Cole will learn new ways of being a ghost (no other choice)
6) New ninja after Nya (Claire)