I know this won't be in 2015, but if they bring back the career mode in 2016, they should give us the ability to create custom teams, build custom cars, a track designer, and let us create our own seasons/tournaments. The career mode should never end, and every year there should be new drivers that come up (randomly created by the AI or custom made by us), and old drivers retire. Most sports games have a lot of customisation features, and F1 games need to catch up.
They should give us a slider, so we can choose how often we want to have crashes/safety car incidents. And they should give us loads of other sliders as well, so each player can create the experience they want to have.