This is fairly close to that functionality -- but not exactly there yet.
What are you looking for in an archive functionality that isn't available (a) via Slack's own export tool (JSON dump of your channel), (b) other O-S archivers or (c) paying for Slack so that you have all your messages available? Ability to archive channels regularly/automatically and search contents (outside of Slack)? That's a direction I've considered going since searching within Slack is IMO a pain.
What are you looking for in an archive functionality that isn't available (a) via Slack's own export tool (JSON dump of your channel), (b) other O-S archivers or (c) paying for Slack so that you have all your messages available? Ability to archive channels regularly/automatically and search contents (outside of Slack)? That's a direction I've considered going since searching within Slack is IMO a pain.