Generally speaking, I think that any game with a subscription should not have a cash shop, and vice versa. (Possible exception for charity events, so long as there is no profit made).
In regards to this specific topic, I would see no issue with items that were a mater of mere chance getting put on the store, while items that require skill or dedication remain off the store.
Example of items that would get put on the store: Rare drop mounts, rare drop pets, rare spawn mounts.
Example of items that would not: Heroic raid achievement mounts, gladiator's mounts, mounts guaranteed to drop from difficult fights, etc.
(No, getting lucky isn't being skilled. You're not a better or more dedicated player because you have a rare mount. When I was playing, I got my riding turtle shortly after it's release in the course of a fishing daily; I did nothing to earn it, and having it didn't make me better or more skilled than anyone else. It's just arbitrary rarity , so the vain idiots who think that something being rare automatically makes it better or more worthwhile have something to brag about.... though I suppose there are enough of those to justify keeping them happy.)
You put me in a bad mood for bringing the headless horseman up. Thats the only reason i keep lvling alts. I even used to ninja people on their daily's :x
OT: I would probably not buy anything from that store since i don't have the funds. Obviously some people will buy all kinds of stuff from there, kids with parents credit cards comes to mind. My guess is that most wow players wouldn't support it.