I've been using Runkeeper for years and years and am really missing the historical weight feature on Strava. This is really great as it helps me keep track of my weight, especially at times when I might want to lose some weight and how this relates to activity increase or decrease. It could also help with weight goals for some.
Ideally, it would be possible to import historical weight from other providers, such as Runkeeper too, so that the history is kept. At the moment I am still using both as Strava just does not have what I want.