The main problem with analytics/metrics is that they're all useless - or very close to it. Each of them is horrible about getting data out in order to correlate it with other services.
If segment.io can consolidate metrics data, provide uniform interfaces for getting data in/out, and can start partnering with other services that should be using this data but can't (there are several dozen), they can turn useless metrics data into immediately (possibly automatably) actionable data.
Just a personal vision, and I have no idea if that's where they're goin or not, I just know that needs to happen, and the team behind segment.io has the chops to pull it off.