With vampires almost certainly spoiled in addition to dragons and cats, who will the fourth tribe be? Vampires are definitely black and could cover red, so my money is on a blue-aligned tribe.
From most to least likely:
>Spirits
>Faeries
>Zombies
>Sphinxes
>Birds
>Moonfolk
>Merfolk (Getting a duel deck, so unlikely)
>Homarids