Flightbeam is doing Frankfurt. The Vote that was going on between KMSP and EDDF was just to prioritize which one will get done first but Mir from Flightbeam confirmed several times that EDDF is officially on the roadmap for them so we will see Frankfurt from Flightbeam at some point
Honestly I hope I will not see it on screens. Developing the god knows how maniest Frankfurt scenery would be a waste of time. Sorry to say it rude like that, but that's the way it is. There are already two excellent scenery developers working on Frankfurt, scenery developers wich you can't beat when it comes to quality.
My advice: cancel this project while you still can and pick another airport. It would be most unwise to continue on Frankfurt.
Göteborg would indeed be a good choice, there's nothing for it yet and nothing in development either, and there's certainly demand for it. But of course there are more airports like that, Göteborg is not the only one.
PS If you'd decide to do Göteborg, I'd appreciate it if you'd do both airports. ESGG Göteborg Landvetter and ESGP Göteborg Säve/City both serve the city of Göteborg and are not too far away from each other, and together they'd make the project almost as big as Frankfurt.