I haven't played Sigmar, but I've heard it praised on various podcasts and it sounds like some of those concepts would be welcome changes in 40k.

From what they put out on the community site about the things they were thinking about, I don't really like the idea of everyone getting daemonic instability. My Guard blobs are going to get whittled down super fast in assault unless Commisars/Priests counter that somehow. And if they do that for shooting leadership too, oh boy. Everything else sounded reasonable. I like the idea of variable move distances. Again, it's probably going to hurt the footslogging Guard army I'm building, but we'll see.