There is a difference to know something will get removed (aka Cutting Edge, 100% dropchance mounts) vs something which is not coming back, without knowledge beforehand.
Blizzard has stated themselves they don't want/like to remove stuff from the game (aka T3, Black Proto Drake are the most famous examples) yet they do it in another way now again. Those are with care "implemented back" into the game via the Black Market Auction House.
This has nothing to do with exclusivity, because I personally don't care if I have those removed appearances, but other's will, since there was no indication that they'd be removed in the first place.
I was merely answering to what the topic is about and all it's different parts, some of which make sense (like I stated) and other's which don't (which I've also stated) for whatever reason it might be.
Back in Vanilla up to Wrath (before the Cataclysm changed the entire world) I knew nobody who had more as 1 character, let alone all Classes and has done Loremaster on all of them. It's more as logical (from what a lot of people suggest here) that if you completed the quest(s) or Loremaster itself, you'd be given those appearances due to the fact they are no longer available. This idea tho would be bad for the current content and game since it's so easy accesible, but 8 or even 10 years back it wasn't as evident as now. Thus to "reward" those who actually did put in effort would make sense. ( at least from what I understand.)
I do agree with you on some part that a lot of the exclusivity would be lost that way, but in Blizzard's eyes exclusivity works differently now. They see it as: you did it before others and managed to "show it off/use it" before others did after nerfs. That's a different way of exclusivity as opposed to let's say 8 years ago.
It's a hard topic to discuss because both ends are right in their own way, and it's hard to make all participating parties happy with any decision which is made.
We'll see how everything works out in Legion (and if changes are made) and give feedback if we notice any flaws. This can be done on the Beta now too, but to a lesser extent due to character copies not working, not everything implemented yet etc.
I do apologise if my writing is a little odd/off since English is not my native language, but I do hope I made my "opinion" clear on this topic . It's always good to have proper discussions and see both sides of a medal before making an opinion.
I don't have a list myself, since I haven't looked into it a lot, but I'm sure some clever people can use the WoWHead database to extract those. Unless WoWHead doesn't have every item ever added in the game (which I doubt) it's possible to do, but not something I'm personally good at ^^.