The problem with the shimmering shadows is that every 7 seconds or so they adjust to the position of the sun. It's not doing this constantly, it only gets updated only every 7 seconds. So the shadows don't move for that interval, and then suddenly "animate" to update to the current position.

That's the problem.

Now a simple fix would be to tweak that interval. I'd rather have these shadows update every 20 MINUTES or so. I'd rather have those shadows look very ugly every 20 minutes than look slightly ugly every 7 seconds.

I don't think there's an .ini setting to tweak this, so this would likely need Bethesda to enable some kind of option. The default setting is very annoying.