Kingpin

Magneto

Leader

Rulk

Exodus

Selene

i would think Magneto wont be a big part if at all because he is already such a big character on his own but so was norman and Doom so maybe, I would have loved to see him on the Cabal board with namor doom emma and the others.

I htink kingpin should have been on the Cabal as well but he would bea really tiny fish in the room metaphorically speaking

Rulk seems like he would hve been handed over to Osborn if he was still working for the government. maybe thats how Norman attracts him if Rulk gets involed, he gets all the comforts he once had by the government. I think that would be interesting.

Magneto and Kingpin would be great.

Kingpin- Would lead to a lot of tensions between Osborn and hima sboth of them try to be the boss.

Magneto - Would never happen. Osborn is crazy but not so crazy to let a powerful being like Magneto in the team. Emma represents the mutants very well.

Leader- Is he even still alive?

Rulk- Dark Reign would go to hell as he kills and takes the power of every member of the Cabal and the Dark Avengers. After that he would kill first the Mighty and then the Secret Avengers shortly before he rips the eye of Aggamoto from Brother Voodoo's chest. Shall I go on? lol

Exocus - If Exodus should participate Norman would have to offer this mutant supremacist a really good incentive. Not impossible but hard to control and even more cocky than Namor.. Doom would hate him and the others as well.

Selene- She and emma would kill each other in the first few minutes I think. And all the others would be happy. lol

sorry but i forgot 3 people

Red Skull

Baron Zemo

Baron Strucker

Baron Zemo would be badass. But he wouldn't return on Norman's side. The Thunderbolt's were originally his and after Norman tried to have Songbird killed (who Zemo had a thing for) and gutted Swordsman, I seriously doubt he'd team up with him. I havent seen or heard of Zemo in awhile. (Exodus is in X-Men Legacy I believe). I doubt Magneto will show up seeing as how most of the Dark Reign series has nothing to do with Mutants (we'll have to see how X-Men/Dark Avengers plays out) cause things could change.

I think Kingpin is too power hungry to really ally himself with Osbourn in any honest way. It would be entertaining to see Kingpin and Norman fight for control of the crimeworld though... 
 
I think Magneto would be more caught up in his own causes, but it would be cool to see him weigh on the situation in one way or another, he's a great character.
 
The Leader and Red Hulk I could honestly care less about...  And I don't know about the last two. 
 
They've already talked about Red Skull inhabiting Steve Rogers mind and leading the Dark Avengers in Cap reborn. Which I personally think would pretty epic. I'm all for that. So much of the MU would get thrown into emotional chaos if that happened, I think. 
 
Annnd I'd really have to think about the last two. It's always interesting to see how certain characters weigh in, though...

The Leader is dead  
 
Strucker is involved (read Secret Warriors. It's freakin mind blowing) 
 
I don't care for Magneto much anymore.... 
 
Zemo SHOULD be involved 
 
The rest.... Meh.