At this point I totally agree with FVD. There is no reason to use Menken, Kafka, etc. for any of the villains that would make up the Six.
At one point it seemed to make sense that to do the Six in TASM3 properly Webb would need to use characters introduced previously, in TASM1 and TASM2, but in many ways I think all of that is out the window.
The viral site already mentioned Otto Octavius, not to mention that the androgenous Dr. Kafka was left in a state where I don't think he should be able to come back. Yes, a bit stupid to have a character changed to be almost what Otto is supposed to be (accent, look, etc.) just to bring Otto in, but hey, bigger mistakes have been made.
There should be no way that Harry would want to work with Menken and give him anything, other than a knife in the back. No, making him the Vulture at this point would be stupid. Yes, many of us believe they missed the mark with Feore, who looks so much like Toomes that it's a waste, but again, I think it's a bit late for that. Guess we can start fancasting Toomes again.
As far as Norman, we know they had the following picture, that was likely going to be a post-credits scene:
The question is whether this will make it into the DVD?
If not, then they likely changed their mind on things, again. If yes, then Norman is definitely coming back.
So, if they bring him back it would likely be in one of these two ways:
1. Turning him into a new Goblin. Maybe this would happen after Harry-Goblin is killed. This idea wouldn't be too bad, I guess, and he could look like this:
#2. Turning him into Venom. They do this I'm done with these movies! I DO NOT want to see Norman as Venom. Give us Brock!!!!! But, I could, unfortunately, see them have the Gentleman drop some black goop onto Norman's severed head and seeing a new body form. Venom needs to be a young character, not some mid-60's dude, so I really hope they don't go this route!
Personally, just leave Norman dead and let Harry be the schemer.