The specific Dark Sky feature no one has cloned adequately is the microforecast that says "it will rain on you in 8 minutes". There's a zillion apps that do a decent job of hourly and daily weather forecasts. But the particular rain warning was something Dark Sky was uniquely good at.

Rain Alarm on Android comes close, and even uses Dark Sky data (for now). But the UI isn't as good and the predictions aren't as accurate.

PS: understand that if you join Apple your work will be consumed and digested by the company in a way that renders your personal identity invisible. This is true both for companies like Dark Sky and for individuals.