Some Sinister 6 suggestions (Because that's apparently still going forwards, albeit in a different way.):
Brian Cox as Doctor Octopus:
Charles Dance as The Vulture:
Need I say more with these two? They're both older guys who play great villains and physically match the characters.
Michael Mando as Shocker:
Perhaps less well known. He's in Orphan Black and Better Call Saul and I've been impressed with him in both. He also plays the villain in Far Cry 3 which I haven't played, but he got quite a bit of acclaim for that. Can play tough and comedic.
Javier Bardem as Mysterio:
He can do weird, I think he's a good fit.
Jessica Chastain as Scorpia:
I've only actually seen her on the help, so this choice is more based on her being rather outspoken about wanting to appear in a superhero movie and the general hype around her joining the Marvel alumni. I think we're bound to get a female villain in the Sinister 6 to mix things up, hence why I've gone with Scorpia over Scorpio.
Karl Urban as Kraven the Hunter:
A talented actor who I think needs more love.