Hearts of Iron IV trailer
Or try to make it happen exactly as it did!
Why do you have to be at gamescom to make a gamescom trailer? This (a very little bit of) gameplay trailer for Hearts of Iron IV asks that. I think we should all shoot our own gamescom trailers, too. Upload 'em and put them in the comments.
If you want beta details, they're here. Otherwise, see an early Hearts of Iron IV preview from the beginning of the year.