But I guess this is an example of if you send to the wrong account that may not have a "buyer". Like what just happened to someone. The ability to cancel the transaction so your funds don't get lost in a random account.
I would keep such a feature out of the core. A user-friendly client may implement something like that entirely in the client - after clicking on send, the transaction goes into a list of "ready to send" transactions, and the user has to click on a second "confirm" button after double checking everything again. And the client may show a warning if the receiving account is not in personal address book, etc.
That sounds good too. We just need some way to help people from getting their funds lost. Since we are all human there are some that will make mistakes.