I was thinking another cool feature they could throw into the DLC... Smoke Bombs - for Theif / Assassin characters..

related to alchemy? or what?

probably it's alchemy because you have to use different ingredients to make the bombs

I'd say that should be left for mods. Unless you can show me mechanics that do or should exist for warriors and mages, I think this would be a little overpowered--there are, after all, invisibility potions which will obscure you just as well.

If enemies couldn't see you, it would circumvent Sneak. One should learn to sneak on their own and get better at it until they can do it in broad daylight instead of hiding in the shadows.

That's just my two cents.

I think smoke bombs would be more for breaking line of sight. Not necessarily for being invisible. I think it's a cool idea and don't see how it could be OP while invisibility already exists using illusion or alchemy. They would simply make it so that you weren't forced to crouch walk everywhere while playing your squishy thief character, because you could have another chance at sneaking after being detected. Much like the final Sneak perk, only uses would be limited to how many smoke bombs you have on you.