Thanks to iBooks, we now have 100% confirmation about the forest spirit rule. Forest strider, 6+ ward save, magical attacks and ItP. It also has the interesting disclaimer that the ward save only applies to forest spirits that are not mounts. My bet is the new stags are forest spirits.
The new Treekin statline is as follows
They are 45 points and monstrous infantry. Can upgrade to a Treekin Elder for 10 points (+1 attack)
Special rules are fear, forest spirit, flammable, scaly skin (x+)
Overall pretty good. T5 MI is amazing in game and now a reasonable price for the Wood Elves. They are the only Elf army with ready access to a monstrous unit type and toughness 5. Unfortunately the scaly skin figure is obscured but looks to be a 4+ save.
Now for the bad news
We have confirmation of no new Wardancers. The existing metal ones have been re-released as a 1 click bundle alongside the new Shadowdancer (resin). This is in the same guise as the Troll Slayers.