Add a "Rest Day" button to Training Calendar
Strava can be addicting, so it'd be good if they made it easy, even congratulated you on taking a needed day off, or a day off when sick. If there were a rest day button, you could click it and it would congratulate you for making the wise decision to take a day off. You could click it and it could even allow you to fill in a blank to say why you're taking the day off, or they could give you some common options for why: "Just needed a day off," "Planned rest day," "Feeling sick," etc.
This is a way to let fellow athletes and followers know why you didn't participate that day. Given the new "Training" log feature, tracking rest days is important. This simple button could make it easier for athletes to take a day off -- when you look back on that day, you'd know why there was a gap (ie "That's the day I was sick," or whatever). Taking a rest day should not be something that gets stigmatized.