Will be possible to have the same key on more than one wallet? On pull request https://github.com/bitcoin/bitcoin/pull/220 say will be possible to import/export keys.
I would like to know if will be possible to have the same key on different wallets and only be able to spend the bitcoins from this key with permission of the other users that has this same key on the wallet. Example:


I have a key on my client with 10 BTC. 
I export this key and send to a friend
The key will be on my wallet and on my friend wallet
When I or my friend try to spend the bitcoins from this specific key, will be requested a password asking if we accept the transaction.


Will this be possible on next Bitcoin versions?
The pull request that you refer to is just for simple import/export of private keys and wallets and does not include the feature that you want.

There have been some discussions on multi-signature transactions which sounds similar to what you are looking for. That would allow for cases where two different private keys are required to make a transaction. See this forum thread and the draft proposal here.