As part of the slack integration we are able to choose from a number of drivers/filters as to when a slack notification is sent.

One of the main reasons we want to notify a channel in slack is that a feature has been made available. Whilst many may consider a status of "Done" to be sufficient, a "Done" ticket in our workflow (and I believe, in jira workflows generally) is that a Done ticket is basically code (etc) complete, but isn't available to users until it has been deployed/released. i.e. for us that means it has a fix version that refers to a release that has, well, been released.
I would very much like, and hope others would also find useful, an addition to the slack filter options that allow us to promote a message to slack when ticket is "released", or at least has a fix version set, as this is the best indicator for us that a feature is available.