[Baertram]

I love the Lotro chat whispers as well but all I could come up with is FCOChatTabBrain which provides as least whisper redirect so if you start to whisper it will change the chat tab to a defined whsiper tab. And also provide auto answering in the whisper channel if you are at this tab then. All you need to do is right click a tab choose properties and only enable the chat category whisper on this one tab, disable it on all others.

And then setup FCOChatTabBrain and select this tab as whsiper tab etc.
It also got sound notifications and auto chat channel and tab switch for other chatsike guild chat etc.
Blacklist, whitelist for sounds like "good night", press return key to answer in last incoming chat channel etc.

Chat history is there already with the addon pChat e.g.

A new Ui like a subchannel or button per whisper recipient (conversation) was on my todolist but the chat Ui is not really easy to extend and creating a new tab only for that was not possible for me so far. Maybe in the future. You can also test TOM, the tamriel online messsenger. Maybe it got such a feature.