Does it make any sense at all for a shop mount to be of a non-unique model? I mean if they put some recoloured thundering cloud serpent on the shop would anyone honestly care to buy it? So maybe they should put a recolour of something rare, like say, the Kor'kron Juggernaut (Garrosh's Invincible)? But then that would totally devalue the genuine article and piss off the people who actually went to the effort of obtaining it. No, I just can't think of any scenario where it makes sense to add an existing model to the shop, so logically speaking, every shop mount needs to be something "new".
Now if they were making "new" shop mount models at the expense of "new" ingame mount models, then I would agree that this is reason to get upset. But you can't go about assessing this by looking at how many new shop mounts there are and then extrapolating that if it weren't for the shop, those mounts would've been available in the game. You have to look at how many new mount models you can get in game and decide whether that number is decreasing. They can add 50 new mount models to the shop for all I care, but as long as the number of new in-game obtainable mounts stays consistent or better than the historical precedent, you cannot argue that the shop mounts have come at the expense of stuff you should have got with just your sub.
And if you look at MoP, I hardly think you can complain about the number of new mounts (ie mounts which are distinctively different from anything from previous expansions) they have introduced:
1) Cloud Serpents
2) Flying Disk
3) Galakras
4) Garrosh's wolf
5) Dragon Turtle
6) Skyscreamer
7) Direhorn
8) Mushan
9) Astral Cloud Serpent
10) Pandaren Phoenix
11) Primal Raptor
12) Yak
13) Scorpion
14) Sky Golem
15) Kor'kron Juggernaut
16) Jewelcrafting panthers
17) Geosynchronous World Spinner
18) Depleted Kyparium Rocket
19) Riding Goat
20) Grand Wyvern
Now you can nitpick that some of these are "just" reskins or whatever, but my feeling is that MoP has offered more new and interesting mounts than any other expansion to date.
But is it appropriate to initiate a backlash for something that you simply fear will happen? I don't believe so. Let Blizzard know what the line is that should not be crossed and respond when they make obvious overtures that they are approaching that line. Blizzard have long expressed the view that their game will not go pay-to-win in the foreseeable future. If/when they declare otherwise, (and at the time it remains something that we don't want - a lot can change in 10 years after all), then by all means, respond accordingly. But really, punishing them for something like shop mounts, a feature that many players actually like, on the basis of an untested theory that they are lying is simply escalating an issue that should rather be left alone.