Any of you who seriously think this film series would go to 6 films are seriously deluded. Sony, Raimi, etc. all obviously want to put the most popular Spider-man villains in here before this franchise ends. Will it make enough money to make 6 films? Probably. But will they? Not likely and if they do it will probably be with a new Spider-man actor, new director, etc. and they know we would all prefer to keep all the same cast and crew involved(which ain't gonna happen).
I think they could've had a 4th film but i'm okay with them throwing Venom in 3. Face it people, after GG and Doc Ock, Venom is the third most popular villain and DESERVES to be next especially if this was the last Spider-man film in the series. If they had a 4th one 100 percent confirmed, i would say yes set him up here and make him the main baddie of part 4, but more than likely, there won't be a 4th one at least not with the same cast and crew.