Ive seen quite a few people running soft cases in E1/8th.
Not sure id recommend it though as any kind of problem, including flying debris (shattered gears, etc) have an increased chance to puncture the soft case. Depending on what you have of course. Seems like most E8 have gears spinning rite next to the battery...
Hard case provides a little extra insurance. I run hard case in my stuff simply because our tracks like to see it.