I think Thunder Lizards should be normal pets as that a lot of exotic beasts appear rarely as mounts as opposed the the family you've suggested. Pterrorwings or Blightbeasts(
http://wowpedia.org/Nerubian_flyer and
http://wowpedia.org/Nerubian_spiderling) would get my votes though, but I'm unsure should Kunchong, Silithids and Nerubian fiends should be grouped together. But then again I would love for more insectoid family, so my suggestion would be that slimmer silithid models should be a group consists of silithid ants and hoppers as well Nerubian Flyers and Nerubian Spiderlings, while Kunchong and Silithid Colossus should be grouped as 'Colossus'. Screw that, just expand the Silithid family to include Nerubian Spiderlings, Flyers and Kunchong since its the only exotic family sans post cata quality models.
Another groupd that I would love to see is Firebird or Pheonix or Roc. But I would happy to see both Thunder Lizard or Pterrorwings family as both family could include post cata quality models.
However, since that we also should take into account of having to be back to Draenor, I would DIE for an Elleks/Mastodon family.
They can be grouped as 'Behemoth'.
Family: Behemoth (Exotic)
models: Outland Ellek, Draenor Ellek and Northrend Mastodons.
Diet : Cheese, Fungus, Fruits, Bread
Skills; Trumpet (Bloodlust), Tusk Attack (Physical Debufff) and Herd Alpha (Armor bonus spec)
Another group I think would be awesome would be Protobird, would include Terrorclaw adult, chick and maybe Dreadraven?
Family: Protobird
models; Terrorclaw chick, Terrorclaw Wings, Dread Raven
Diet: Meat, Fruits, Fungus, Bread
Skills; Tailwind (Haste Buff), I have no idea about the rest, maybe levitate?
I would also like to suggest some fix for current Exotic family skills as some are just tad 'aesthetic'.
Both Worms and Chimera's aoe removed. Chimeras get 'Guardian Wind' (levitate) and for Rylaks, their Levitate would cause them to 'fly'. Worms 'burrow' changed into its own version of deterence. I would also suggest that Devilsaur's feast to removed/changed into 'Chomp'; When the devilsaur's life is lower than 50%, its basic attack would return 2% life, lasts for 8 seconds. But I DO LOVE the idea of our pets eating our enemies so I suggest the current 'Feast' changed into a minor glyph.
"Feast"; Your carnivorous and omnivorous pets can now scavenge on the remnants of your enemies, returning x hp and x focus, while your herbivorous pets can graze for the same effect.