Yeah, I built (and later shut down) didlog http://www.didlog.com/ a while ago which I had hoped would eventually turn into something like this. Track code commits, calendar events, emails, files changing, etc to try to put together a map of everything you're working on.
I knew I'd be biting off more than I could chew if I tried to tackle time tracking from the start so I was hoping I could build something useful before moving into that area. Turns out, I couldn't (given my limited time and resources).
It would be awesome if WakaTime and others provided some way of interfacing with an API, so that individuals could track time in a way that made sense for them while reporting in a relatively consistent standard to a central system used for accounting and billing.