The lizard would be cool, They did mention Dr. Conners in the first and showed him in the second, so its possible they use him, but use him or not, i think they should have set up his field of research some more in 2 when they showed him.
I would love to see venom, but that would really need to be 2 movies and thats if they portray it in a similar way that they did in the 90's cartoon. Plus they could have brought the symbiot back during 2, not that they still cant do it, but if they do its looking like they wont use brock, he only had a passing mention. They have JJJ's son's set up in a position to hate Parker already (Brock hates Parker, Symbiot hates Spider-Man) so they may twist venoms character that way, which i would be against (dont think they should change the origins of the characters too much) Though there is also very strong set up for Green Goblin 2. I dont think they will really push that off with the setup they gave it, but they might (wouldnt be typical hollywood though) which would be nice. My fear is that they give him 2 villians to fight, which doesnt generally seem to work that well.
The other thing to consider is, if im not mistaken arent the actors only signed on for 3 films? Im not really a fan of the changing actors in the middle of a saga. So if they only go with 3 then its more reason they wont do venom, unless they do it in one film which i think will mess it up.
-Darth Simon