I have just read through the acrimonious debate headed Just in case, which has highlighted another shortcoming in the implementation of email notifications. At http://forums.adobe.com/message/2289878 , John Joslin starts off saying I find it a pain to have to read through your long and rambling homilies... But there is no way to work out from the email who he's complaining about, and it could be any one of the contributors to that thread. Until proper headers are introduced, would it be possible to include in the email a reference to the post (message no.) being replied to? That would make far more sense than the current line reading This message was sent to: ..., which doesn't tell us anything we didn't already know.
Maybe. On the other hand I only use forum view and I didn't know who he was talking to either. Only when I realised this did I look at the 'in reply to' text.
I never use threaded view, and most times just tack my reply on the end. If I think it's not obvious who I'm talking to I include a brief quote or say @joe bloggs.
This is how it used to work before we had threaded view and it mostly suits me fine. On the whole just a continuous flow of posts is easier to quickly read through, with clarifications such I describe when needed.
From a technical point of view what you are asking for is easy. The message object has a property telling which message is its parent so you just have to generate a link inside the email message template. Then again, adding proper headers is just as easy from a technical point of view.