Will it be possible to export a key and only allow it to be imported once? When the import/export key be implemented I would like to know if it will be possible to export a key with an option like: The exported file can only be imported one time, or that the exported key was exported with an option that removed the key from the wallet that exported it. I ask this because I would like to receive for example a exported key file from someone but with the certainty that the key is not on this someone wallet anymore (or any other wallet).

Will this be possible?
No, there is no way to keep track of what people do with their private keys. You could easily write down the key before exporting it and you can use it without ever importing it to a wallet. It's possible to construct a transaction from the private key manually or using some 3rd party software and then broadcast that transaction to the network.

It sounds like you want to be able to send money without using the blockchain by simply passing private keys around. You then run into the double-spending problem. This is exactly the problem that the blockchain is solving. So, no, if you want to securely send bitcoins you will have to use the blockchain.