I'm with Brother Tyler here - I think Bladeguards will be to the Primaris Dark Angels what Company Veterans are to the Firstborn Dark Angels. They'll be highly decorated / experienced Primaris, who fight either in the Command Squad, or as part of a single squad in one of the 4 Battle Companies. I don't think they'll be Deathwing, because I don't believe they fit the modus operandi of the Deathwing - a heavily armoured, surgical strike force that deep strikes in a unleashes an extremely focused fury. Deathwing Assault allows you to teleport in and fire twice in one shooting phase with storm bolters, assault cannons, cyclone missile launchers, plasma cannons...if you're going to incorporate the Primaris into the Deathwing, then I'd be amazed if you just gave them a shield, sword, no teleport ability and let them get on their merry way.
Aggressors have always seemed a more likely Deathwing option, given their firepower output, melee capabilities and even toughness - albeit through T5 rather than an invulnerable. However, the issue here is lack of teleport ability. But here's an option: we know that the Dark Angels have historically kept their distance from Mars, favouring their own Terran technology. There is also mention in the recent lore that they're trying to learn as much as they can from Cawl to stop them being reliant upon them. Is it possible that Dark Angels techmarines might be able to develop their own variant of Gravis armour to award those Primaris members of the Deathwing? It would certainly allow the Deathwing to retain its uniqueness relative to the other Space Marine 1st companies.