Is it currently possible to add voicemail transcription and send in an email with thirdlane?
sorta. This is done with a 3rd party service. Usually the way it works is that service sets up an email account..
which you point back to the user's actual email address. Then in thirdlane's VM -> email setting you use the email@example.com address. The 3rd party service will transcribe the message and forward the transcription onto the email address setup in its settings.
Thirdlane/Asterisk Support available