You cannot get these data.
There are several issues with plugin usage tracking:
- No clear definition of a user: Think multi-site, local installations, intranets …
- Privacy: You would have to ask the user before you can activate tracking. There are many good reasons not to send any data to an unknown entity without consent (traffic, sensitive information).
- Different laws: In Germany I need a double opt-in just to send comment notifications. Other countries require different procedures. And you need a privacy policy that every user can understand (good luck translating that!) and that doesn’t break any law. Even Google Analytics cannot do that.
A unified API in WordPress itself is almost impossible and very hard to support. Don’t expect that to happen.
And finally: You don’t need that information. Write good code, ask for feedback, but get used to the fact that most users just don’t care about your curiosity. Use your bug tracker or other feedback to improve the plugin, not statistical data.