So, for those who haven't gone thoroughly over everything we know definitively 7 of the 8 returning Skylanders and in all likelihood the 8th.
Air: Hurricane Jet-Vac
Earth: Shark Shooter Terrafin
Fire: Eruptor
Life: Sure Shot Stealth Elf
Magic: Unknown, but likely Spyro given "textual" mention
Tech: Double Dare Trigger Happy
Undead: Rollerbrawl
Water: Deep Dive Gill Grunt