Draig - I'll provide some background so that you can (hopefully) understand why this is not likely to change.
There is a fairly major problem with sending the contents of a PM in the body of the email about the PM - people respond via email instead of responding to the PM, which means that the original sender does not get to see the reply. With the current system, there is at least one person a week who gets the email, reads the PM, then responds via email system instead of through the PM. I do not understand this, and I am concerned about how much worse this would get.
If we were to keep the idea of PMs then we might consider using some sort of tracking information in the body or the subject of the PM so that we can automatically redirect the response back to the original recipient.
This would be difficult to do as doing so would increase the chances of the email being considered spam.
This would require significant development effort for the already overworked volunteers who work on the JForum codebase. I can't see this being a priority.
We are considering a replacement to the PM system, but more about that when (if) it eventuates.