I spent way too long doing this, and I probably missed something, but I browsed through a very, very, VERY large amount of wowhead pages and wikis to try and get into the minds of whoever is behind the dragon pets. With what we know so far, and other than what Wain has already posted on the Lesser Dragonkin page, it's safe to say that these have the highest possibility of being tameable;
- Proto-Drakes, as most are wild animals that run on pure instinct
- Vorquin, which are obviously quite desired
- Kirin, which were replaced by owlsteeds in Shadowlands. BRING THEM BACK!
- Stone Drakes, as they are just as draconic as veilwings
- Storm Dragons (Cata), for the same reason as above
- Storm Drakes (Legion), as they're basically feral animals, but there are quite a few that can speak and have sapience.
These are definitely possible, though aren't exactly dragons or draconic in any way other than similar morphology;
- Wilderlings, as they're BASICALLY just cloud serpents that attend furry conventions
- Soul Eaters, both winged and wingless
These are almost guaranteed to never be tameable, and are significantly more unlikely than anything above;
- Any whelps from the major flights
- Infinite flight, as they're bronze dragons that have incorrect opinions
- Nightmare flight, as they're green dragons that don't have their blankey or teddy bears
- Chromatic flight, as the only living examples are Chromaggus and
Chromitus from island expeditions
- Twilight flight, as they're test tube babies (rude, I know, but true) recovering under the wing of Wrathion.
- Void flight, as they're also being rehabilitated by Wrathion. I don't think any exist in the wild outside of scenarios we've all done already though.
- Dragonmen, like the crazy alchemists who served Nefarian.
- Drakonids, as they're people with a culture.
- Wyrmkin, as they're just centaur drakonids.
- Saurok, as they're...people? Close enough?
- Tarasek, as they're basically Dragonflight's Saurok.
Lore-wise, these ARE dragonkin, but making them require the book/tome/item to tame would be a pretty cruel move;
- Dragonhawk, which makes some sense I guess
- Drakeadons, which I was surprised to find that the concept of them being mutant core hounds is pure speculation and not a fact
-
Proto-Nether Drake, which is an unused Outland basilisk skin that's labeled as dragonkin
- Would be classified as undead, but are absolutely unlikely since every example comes from a mature dragon;
- Every skeletal dragon in the game
- 0.000000000001% chance of being considered;
- Any adult dragon from the major flights
- Any drake from the major flights
-
Aberration, basically frankenstein drakonids.
My guess? We'll likely only have cloud serpents, hornswogs, veilwings, fey darters, possibly fey drakes, vorquin, and possibly wilderlings and/or proto-drakes. I can't really see any of the other dragonkin creatures being tameable, and I really don't see them putting soul eaters in the lesser dragonkin family since they aren't even dragons. Those should be spirit beasts since they don't fit into any category at all.