It would be really nice if Apple could add a variable delay to the sending of a message to facilitate the inclusion of an unsend button
like Gmail has. Unsend was one of the only nice advantages of AOL back in the day, and while I know we can't have AOL style unsend it would be nice to have the Gmail style delay.
I recently sent out a message to 14 recipients that I should have BCCed and failed to do so. It wasn't that big of a deal - no one complained, and I didn't realize my mistake until a few minutes after I sent the message so this feature would not have helped me. But under some circumstances delaying the sending of a message by some short period of time to allow for unsending it would be a good thing, IMO.