I dig where this is going
The actual start of this arc was Amazon Lily, featuring the Blackbeard Pirates trying to obtain Boa's Fruit, and this is where the Seraphim were first introduce.
What are the three groups we haven't seen since Saturn showed up?
1. Lucci and Zoro fighting in the upper area outside the lab the Seraphim are in
2. The Seraphim (+Kaku, York, and possibly Stussy) in the lab
3. The Blackbeard Pirates (most likely Laffitte and Catarina) not yet shown
Blackbeard isn't the kind of guys that gives up. York called up Blackbeard after finding out the government was making moves on Egghead as backup, offering him the Seraphim as a prize. This gives Blackbeard what he wanted; Boa's Fruit, but in the form of a godlike cyborg. Laffitte and Catarina snuck up when Edison shut off the Frontier Dome to let the Stella, Sanji, Franky, and Atlas down to the Fabiophase, and have freed York and the Seraphim.
Blackbeard stays scavenging. This is just what he does; the Marines are trying to kill a powerful group of people? Swoop in and steal what ya can, retreat when it gets dicey.