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.
Clé du Sinistre écluseur (BRD)
Secret Safe Key (BRD)
Clé du gardien noir (BRD)
Clé de coffret à relique (BRD)
Jump-a-Tron 4000 Key (Nagrand)
Clé du butin des Kolkar (Barrens quest)
Clé de la prison de l'Ethereum (Netherstorm – Blade’s Edge)
Clé du capitaine (Tanaris)
Any Blacksmith keys (e.g. Titanium Skeleton Key)