Personally I absolutely think a sinister 6 is possible. If done in a late enough movie, you'd have a lot of the necessary origins sorted out. Couple that with the secondary villians who you don't have to tell much of a backstory for (ala shocker, or rhino). If they had the rights to Kingpin that'd be a nice change for the movie. It's not only "I've got 6 super powered dudes to try and fight" but also "Who could possibly have the influence to bring these guys together. Who's pulling the strings?!" i'd love it.