"external command" Effect

It would be nice to be able to insert an "effect" into a cell that, when encountered, would execute a user-supplied command.

User replaceable string holders would REALLY be slick.

Some potential use cases are:
- update a message sign with the title of the sequence playing (ie.  c:\sign_utility\message "You are listening to %title"  --- this would display "You are listening to Wizards in Winter"

- update a home automation system to turn off outside lights at the beginning of a show (ie.  "c:\x10\firecracker OFF G10")

- play a sound effect at a specific point in a sequence (ie.  mplayer "c:\my effects\scream.wav")

- update an RDS transmitter with the current song playing (ie. rds "%title by %artist")

the possibilities are endless....

We have this on the list for version 2.  There will have to be a security token implementation for it, else someone could share a sequence that includes a nasty command (e.g. FORMAT C:).