So, just as a reference here are the keys we're currently seeing as ones that will not be converted to gold or removed upon release of the patch -- if you have them they'd be put back into your normal inventory. This isn't necessarily a final list, and it's possible we could cut the list down even further before 4.2 releases.
험상궂은 주정뱅이 열쇠 (BRD)
Secret Safe Key (BRD)
암흑의 문지기 열쇠 (BRD)
유물 금고 열쇠 (BRD)
Jump-a-Tron 4000 Key (Nagrand)
콜카르 노획물 궤짝 열쇠 (Barrens quest)
에테리움 감옥 열쇠 (Netherstorm – Blade’s Edge)
대장의 열쇠 (Tanaris)
Any Blacksmith keys (e.g. Titanium Skeleton Key)