Thanks for updating, great list except for the flagrantly offensive omission of beavers. :O
Seeing those scythehorns, there are some amazing color combinations that haven't been used yet. I especially love the dark with purple and the brown with blue. I really hope they consider a future family for those.
And honestly we don't have many left. It would be relatively easy to account for most of these either as a new or move into existing.
New challenge family, Elemental: Elemental birds, gyreworms, hell hounds
Undead: Bone carrion bird, skeletal raptop/windserpent, ghost pets etc
Leatherwings: Pterodactyls / Skyscreamers / Pterrordaxes
Hornsteed/Hoofsteed/Somethingsteed: Dreamrunners / Scythehorns / Zhevras / "Unicorns", Horses, Windsteed
Tuskface: Elekk and Mammoths, move shoveltusk to it
Cloud Serpents: Not touching that one with a 10 foot pole
And they could easily finagle some of these into existing families or make branches.
Crocolisks: Diemetradons / Incendosaurs
Riverbeast: Frogs/Beavers (similar to the clefthoof/rhino relationship)
Goat: Rams
Silithid: Kunchong
With the exception of ones like camel or cloud serpents, I could see these being perfectly viable.