I think it would be a good idea to add /reply so you don't have to type /whisper player everytime someone talks to you
Reply only whispers to the person who whispered you last
Type /reply again to turn whisper chat off. Only works when you have typed /reply to reply to someone.

Well?

I like this idea very much

I can see how inconvenient that can be when many people are whispering to you, and you're in the middle of typing a long response (multiple lines worth). It can prove a security issue when dealing with Operator/Admin matters too, and since you have no control over who it replies to, anyone could override your command just by whispering to you.

Whisper does use halfnicks, so you don't have to type their full name. Just prefix your text with @[name] - @zion will whisper to ZionFox if they're online, @scop will whisper to hardscoping_king if they're online too. It's far easier, and more secure since you know who the message will go to.

Ahhhh I see

What if you typed /reply then it said: All messages will be sent to [player] (Where [] isn't used)?

It could still be overridden if you take your time sending the command by other people whispering to you.