Average heart rate (moving only) and total average heart rate?
I don't know for an absolute fact that Strava is displaying my average heart rate over the full time of the activity, rather than just for the moving time, but I rather suspect it is, because on rides where waiting at stoplights and whatnot takes up more time it seems my heart rate average for the ride is unexpectedly low. While my heart rate will lag behind my actual effort for some short distance after a light turns green again, I don't believe that this accounts for what I'm seeing.
So I guess the first question is: is the average heart rate displayed for a ride including all heart rate data, even during periods where I am not moving (but my heart is still beating)?
If the answer to that is "Yes," then I would suggest that you display two separate average heart rate stats. These would be the data your currently display, ie: the overall average heart rate, and the heart rate only counted during times where I am moving. This would be similar to counting average speed only over the moving time, not the elapsed time.
The reason why this information is important to me is that I do quite a lot of training rides where I set a heart rate target and try to hold as close to that heart rate as I can consistently throughout the ride. On some of my rides there are some intersections where I sometimes get stopped by a traffic light, and the amount of time I spent just standing over my bike waiting for the light to change gives me "resting" time where my heart rate drops significantly. Factoring this time into the ride obscures how well I kept to my target heart rate over the course of the ride. As it is now I only really trust my average heart rate data on rides where I simply lucked out on the traffic lights and never really had to stop.