I have been using an A7S for about for about 3 months now shooting a mixture of run and gun interviews, studio interviews and sports (soccer, basketball, volleyball, pro rally). The rolling shutter hasn't been as big a problem as I thought it would. Yes, if you whip pan or shake the camera you will see it, but if you it's properly stabilized it isn't a problem. Even shooting handheld run and gun is fine. In APS-C mode it's much better which usually works better for sports in order to get additional reach, but even shooting basketball handheld in full frame wasn't a problem. 60p also further improves rolling shutter.
That being said the image off the A7S is just incredible and even the internal audio quality is very good which now means I can do run and gun style shooting without worrying about an external recorder. That in itself has greatly simplified my life. I have also used it during a pro rally shoot while it was raining. Although I was conerned it wouldn't take it I had no problems and feel like it's pretty resistant to rain.
Also, being lighter and smaller means it's easier to carry which is a plus on long shoots. But at the end of the day it's the quality of the footage that counts and the A7S delivers. And don't forget about the low noise. Need to shoot documentary style indoors without additional lighting? No problem.