These large open world games would be great for episodic content. I am still not sure why someone hasn't really done it, especially with GTA or a super hero game like Spider-Man.
You buy the main game and it includes:
- 25-30 hr main campaign, along with all the other fun activities
- access to the first "episode" that comes out 3 months after the game, to give people an idea and a hook to get the rest.
You then sell season passes, which include 3-6 episodes through a year, that equate to another 25-30 hr campaign, within the same open world. They could retail for the same amount as the main game, because the content, stories are equal. Sometimes adds new locations and such. You do this for the next 2-5 years as the true sequel is made.
With this approach, you could easily have the new seasons focused on new characters, including playable ones, who interact with the old cast of characters all within the same game world. Going the super hero route, if done right, you could get a huge build up, Avengers style, with a host of characters finally coming together by the 3rd or 4th season. You just have to have compelling writing, and a gameplay loop that will keep people interested in the game, season after season.