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.
Llave de Tragapenas (BRD)
Secret Safe Key (BRD)
Llave de guarda oscuro (BRD)
Llave del arca de reliquias (BRD)
Jump-a-Tron 4000 Key (Nagrand)
Llave del botín de Kolkar (Barrens quest)
Llave de prisión de El Etereum (Netherstorm – Blade’s Edge)
Llave de capitán (Tanaris)
Any Blacksmith keys (e.g. Titanium Skeleton Key)