I couldn't find a thread like this but perhaps I'm not using good search terms.
I feel it would be handy to start a list if there isn't already one of everything that will no longer be obtainable or may become significantly harder to obtain when mop hits.
This would include items, achievements, achievements becoming feats of strength, titles, mounts, pets.
For example I believe there is a tabard from scholomance that will no longer be obtainable and must be farmed beforehand.
Anything else that is known about I'd appericate it if you'd share your wisdom.