What Achievements, Titles, Items, Mounts and Pets, (etc.) Are being removed in Patch 5.0/Mists of Pandaria?

One thing that has been confirmed by Blizzard as changing is the drop rate of some raid mounts will decrease on release of Mists of Pandaria, specifically Smoldering Egg of Millagazor and Life-Binder's Handmaiden, both currently 100% drops on heroic raid encounters.

As far as we know at this point there are no dungeons being removed, no old questlines being removed and no old reputations being removed. Almost all new content, with the exception of Pet Battles, the Fall of Theramore and Heroic SM and Scholomance, is Pandaria-based. As far as we know, achievements, titles, mounts, etc, will remain achieveable with the usual exception of the rotating PvP mounts.

Doing a comparison of data-mined Feats of Strength backs this up, with only new Realm Firsts, new expansion Feats and the PvP stuff the difference between the current list of Feats and the list for Mists.

Decided to post this as an answer, since it technically is.

While there aren't any absolutes on what will be changed or removed, we do know what will be getting makeovers, and we know how things worked in previous expansions. Although that still doesn't help much with solid answers, a list of worthwhile things that may be changed or removed can be generated to help prepare yourself just in case.

I've made such a list, and it's hosted at Wowhead. Remember, this is just what may be changed. It is not complete and it is not final; it's just a tentative resource.