You can sort of do that now if you're running iOS 9. In the upper right screen of the daily activity report there is an icon. Press than and it will let you share your progress with others via text, email, or twitter. You can also copy it to notes or print it. If you want to share just a workout (say a run), just open the run stats first and then press the icon in the upper right hand corner. Now you can send the results of that particular workout.