Lizard on a Sinister Six team wouldn't work. Especially on film. It would be near impossible to get him to work with other villains. I didn't even like it on the Ultimate Spider-man cartoon. Lizard may have been in a film already, but it would be silly to have him as part of the Sinister Six.
Having a couple of villains back story covered by previous movies is a good idea, but not all of them have to have been introduced already. Not every villain needs to have an entire film dedicated to them to work.
Also a female is currently a member of the Sinister Six. A female version of the Beetle. However, the character and the current iteration of the Sinister Six seems to be a joke version with the sole purpose of being the whipping boys/girl to the Superior Spider-man.
Guess I should have specified any of the original incarnations of the Sinister Six. The latest S6 is kind of a joke compared to the originals, including the Sinister Twelve...
I do agree with you that it helps to have one or two villains explained in the movie, while the others could be introduced/explained in the prior. So if the S6 turns out to be where they are going, as I believe, and it's now effectively a 2 parter (TASM3 and 4), then we could already have Rhino, Electro, Green Goblin, maybe the Vulture, Lizard and/or Black Cat.
Yes that could be the Six, but as you say certain members make more sense than others.
Vulture, for example, just has to be a member. As I've been saying all along, the moment Adrien Toomes is introduced you know we're heading towards an S6. And although it looks like Adrien might be introduced in TASM2, that doesn't mean that the Vulture will be. That story could be shown at the start of TASM3, very easily since Toomes would have already been introduced...
I do feel that Black Cat is a special character that has to find her way into this fanchise (and I think Felicity is going to be it). The other female villain you mention, the latest version of the Beetle, isn't a known villain and is very unlikely. Definitely not a top 10 Spidey villain, and likely not even a top 20. But Black Cat is up there and we need other strong female characters in these films once Gwen kicks it. Again, having Black Cat as part of the S6, initially, but turning on them, just makes good sense and allows the S6 without having to battle all 6 in one fight. Her switching and taking out the bully Rhino or the crazed Vulture (I could see her jumping on his back and covering his eyes, making him crash), ends up dealing with 2 out of 6.
I think a main question though is whether both the Rhino AND Electro would make it through TASM2 to be members...
It's hard for me to think they wouldn't want to use Electro in the Sinister Six since his powers and look are so special, but would you really want all of the threats from TASM2 back in TASM3?
If you look at most Super Hero movies nowadays, the villain usually dies.
- Spiderman 1, Green Goblin died.
- Spiderman 2, Doc Ock died.
- Spiderman 3, Harry died and Brock/Venom died (Brock definitely, Venom maybe).
- Batman Begins, Ra's died.
- The Dark Knight, Two Face died.
- The Dark Knight Rises, both Bane and Talia died.
- Ironman, Stane died.
- Ironman 2, Whiplash died.
- Ironman 3, the Mandarin (the real one) died
And so on, and so on.
In fact, the only two movies I can think of where the main antogonist did not die was X-men (Magneto was put in prison) and The Amazing Spiderman (Lizard put in prison).
So, will Electro and Rhino both survive TASM2 to be able to be part of the S6?