There are two functional areas of scripting being discussed here. Being able to move and sort mail from the PowerTalk Mailbox which is a function of Finder scriptability, and the AppleMail application, which is a text editor with a PowerTalk mail header capability.
AppleMail is not scriptable, script aware, or recordable. AppleMail was never meant to be THE messaging application, it is a bare bones tool. AppleMail as a word processor will probably never attain the scriptability of say, Scriptable Text Editor. In other words, everyone should think of AppleMail as the TeachText of messaging.
If you need a scriptable word processor, then MacWrite Pro, WordPerfect, or Microsoft Word as well as other are all candidates. These three all support AppleScript and PowerTalk mail headers.
The Scriptable Finder can be installed into the System 7 Pro environment, but the capabilities of managing mail through AppleScript are still extremely limited. New Mailbox APIs will be made public to enable development of better managers and filters for the PowerTalk Mailbox.