WARNING! Spoilers about the bosses will be discussed in this post. Avoid reading!
OK, so maybe, just maybe my theory of MGS4 is correct. Dead Cell was a group of people who were dead and brought back to life through some new genetic technique. Or, maybe it's just Vamp. That's why in MGS, FOXHOUND wanted Big Boss' body. They wanted to use Dead Cell technology to bring him back to life. I didn't understand why they wanted it for more genetic testing when they already had his DNA and genetic traits used for the clones. That just didn't make sense.
Now, with the bosses revealed, it could be Dead Cell reanimated versions of Psycho Mantis (Screaming Mantis), Decoy Octopus (Laughing Octopus), Sniper Wolf (Crying Wolf) and Vulcan Raven (Ranging Raven). Screaming, Laughing, Crying and Ranging. Similar in theme to The Joy (Laughing), The Pain (Screaming), The Sorrow (Crying), The Fear(?) and The Fury (Raging). But, they could just be new versions of the old FOXHOUND crew. In fact, I do think they are new and not reanimated former FOXHOUND members. But, I like how Kojima pays respects to both MGS and MGS3 with the bosses' names. For example, Crying Wolf = Crying, an emotion like the boss names of MGS3 and an animal name, Wolf, like with the MGS bosses.
Many are starting to balk at the idea of reanimated former bosses, and I agree, it seems cheesy. But, you never know. It's Kojima we're talking about.
EDIT: The title for the new bosses is "Beauties and the Beasts." It looks like Screaming Mantis and Laughing Octopus are female, and Raging Raven appears to be male, but what about Crying Wolf? Male, I guess. One thing is now sure, they aren't reanimated versions of old FOXHOUND unit members.
Weapon wise, it looks like the following...
Crying Wolf = Rail Gun or maybe a rotary cannon.
Raging Raven = Milkor M32 Grenade Launcher
Screaming Mantis = High Frequency Katana
Laughing Octopus = Large Knives (one for each tentacle)