The current broadcast deals have years left before they expire so the venue has no bearing on the billions the NFL gets annually from the various broadcasters. The networks do have certain technical requirements to support modern day telecasts, so there may be an issue with some stadiums around the country in that regard.
As you implied, the big issue is the local revenues generated for teams at their home games. Corporate sponsors, suite owners, etc. pay a premium for home games and while ticket, concession, parking and other local revenues pale in comparison to broadcast revenues, they are still a significant factor to team bottom lines.