I have my Android device set to use en-GB as its primary language for metric units, my spell checker is set to en-US, and my Google News is set to India.

What you want is already possible. However, I do wish the platform allowed a more direct customization of all LC_* stuff.

> Windows has been getting locale settings right for ages now.

Do you mean Windows phone? If so, I'm impressed. If you meant Windows, the computer OS series, well, that would not be a fair comparison for Android. Linux already gets that right.