Yeah, I think Dreadnought is already 'all-in' and going with Lazav as well is a recipe for losing to variance. It provides an avenue for protection, but I can already get that with Thoughtseize/Force/Daze or just jamming 7/7 Shadows if they die.

What I like about Ub Shadow is the velocity, playing 8 cantrips and 4 'free' cyclers that enable your biggest threat. Stifle is a card that can push tempo with mana-denial while also enabling a 12/12 trampler. It's also a Force of Will + Daze + Thoughtseize deck, which means protecting the combo should be pretty easy to do. I love to jam bad synergies sometimes but this one has a ton of overlap that I think could make it viable.

Regarding Dreadstill: I think the weak point in that deck is Standstill, which is metagame dependant. I have a notoriously blue-light metagame where it just doesn't pull its weight. There was a recent 1K and there was only 4 copies of Brainstorm in the top8. I think replacing Standstill with Dark Confidant for the needed card replacement from playing Force + Dreadnought could be potentially powerful. He's playable when fighting from behind in the game and even can absorb critical removal spells from opponents, all the while supporting the Death's Shadow plan by using life as a powerful resource. I am strongly leaning towards Confidant over Street Wraith.

There have been several Force of Will/Dark Confidant variants in legacy, I mean Team America used to be a premiere deck. The worst part of that setup was blind flipping Force of Will from a Bob trigger. Now it actually accelerates the Death's Shadow plan.

Listen, I'm not saying 'this is the best deck ever'; but I am saying this seems to have some serious potential because of the strong synergistic overlap of the cards.