Making enemies that stalk the player is actually quite easy in itself, all you have to do is make a package to follow the player, and have it on 24/7. There's an added layer of complexity though, how do you make the NPCs wait until the player is no longer in sneak mode to resume pursuing the player? The reason for this being, a lot of players probably won't like psychic clairvoyant enemies who constantly stalk them, and always see them no matter what, and unless they hypothetically travel really really slow all over Skyrim, and perhaps never swim, and never unstealth to talk to NPCs /etc/, they're gonna HAVE to come out of sneak SOME time... And that would be ideally when the danger would arrive.
If this is possible, can someone please explain step by step how to achieve this?