BGP Flowspec
An example of how an advanced hook action to a Script would be useful is to allow users to implement their own BGP Flowspec rules themselves.
As far as I can imagine, if today there were a { [actions] } in /routing/filter/rule that allowed a call to a script where the debug.fwp-ptr attribute was passed as one of the call arguments of the script, it would be possible to create a set of scripts in which you could create dynamic entries in /ip/firewall/filter/ and /ip/firewall/raw/ to then have very similar results to the BGP Flow Spec protocol.