I don't think we'll support that Segment use case for a while since it involves storing raw user event data ourselves. Most companies have some sort of data warehouse already that Segment writes into and that's the level where we integrate currently (Segment writes raw events into a data warehouse, we pull aggregate data out).
For Slack, I don't have a specific timeline right now, but likely will get to that within the next few months. There is a workaround today using our webhooks, but it's not as smooth as a built-in Slack integration.