Yes, and this is this patch that made me think about implementing it
The only problem I see is that it requires to build bitcoin and it's dependencies
When I tested to build bitcoin it was really a pain (Ubuntu), so I think building it without internet connection must be even more boring
Why not put it into the official distribution? I think all you need to operate a completely offline wallet and make it easy would be an ability to export/import the latest blocks and to export/import transactions (on import, the client would just behave exactly as it would if it had received the transaction from the network). For the blocks, if the export could just export the blocks downloaded since the last export, it would probably make it quicker to keep the offline wallet's blocks updated.