I played a couple of hours of Survivor difficulty on IWBUMS 41 and I am thoroughly impressed! There is a very nice difficulty curve going on if you play in Rosewood or Riverside, but starting out in Muldraugh or Westpoint is masochist mode. There is a very heavy density of zombies in the big cities, and I think newcomers/old timers new to the system will have a very tough time with those places. I certainly did.
The sneaking mechanic is amazing and sneak running saves lives. However, I do have a concern/suggestion - the old sneak key, or "aim" key now, control/right click, completely takes you out of sneaking. This means, while crouched down you have to move in the direction you want to look at instead of standing still and pivoting to look. I'm not sure if this is an intended nerf on sneaking as it's pretty OP, or if sneak pivoting is something overlooked. I would think that separating right click and control keys could fix this if needed, such as right click for pivot only mode and control for the stand up and aim weapon mode.
Or this could be left as is, it's not really a big deal, just a quality of life opinion on the sneak mechanic.