I think Kraven has a strong foundation already though. Things can be tweaked here and there, but overall a strong base. It's usually "his look" is the reason as to why people say he wouldn't work, yet that is the simplest solution.
After Green Goblin, I don't think any villian has the potential impact of
Electro (Venom if he's done right). Not only as he relates to Spidey in terms of danger, but in terms of his potential reach and magnitude on a story as a whole. Electricity is the lifeblood of modern civilization. He can override and manipulate electrical systems. Chaos and social upheavel at his fingertips. Send New York into the dark ages. People turning against each other,fearful of each other etc.
And his powers and how they can manifest themselves would be incredible from a visual
stanpoint. Not just electric bolts from his fingertips, but blowing out walls, floorboards, ceilings. Blowing up cars. I believe he has some control over magnetic fields as well. So much possibility.
Scorpion is unlikely for a sequel because he is too similar to the Lizard in how he would look in battles. In fact I think it's almost a guarantee he won't because of it.
We know GG will be in this series at some point, most likely the third.