The Lizard
Who should play him? The obvious choice would be Rhys Ifans, who is already established as this series' Curt Connors/Lizard. It'd be rather stupid to recast him since he did a decent enough job last time round. Still, they recast The Hulk for The Avengers and that turned out just fine, so who knows? It doesn't seem like his heart is in reprising the role, so maybe it could be someone like, say, Bill Pullman? Based on his work with David Lynch he's multifaceted and a leftfield choice, but based on his drop in profile as well as his recognisability from the likes of Independence Day, he is also a safe and low-risk choice at the same time as bringing something unique to the role that wasn't exactly beloved in the last film.
Why would/should they be included? It would make sense that The Lizard be included in this Sinister Six, as he was a major villain in the first film and integral somehow to the whole boring conspiracy surrounding Peter's parents and their dark past. To drop him in favour of establishing a new villain seems a silly thing to do. The Sinister Six would be better off with him in the gang for his knowledge of Spiderman's alter-ego. Who knows? Maybe this time he'll grow a snout and wearing a lab coat!
Likelihood: 3.5 out of 5 It would make sense, but then who knows what goes on in the mind of Avi Arad? I'd be up for giving The Lizard another chance to shine. But please, if this comes to fruition, can someone chuck some more of the budget at The Lizard's CGI? Please? Or, hey, use more practical effects?