One thing that you can be sure of, is if they do Germany, the Nurburgring won't be there, not sure why people think it would be. Just isn't in the Horizon MO.
If they do Germany, it'll be part of a multi-country thing akin to FH2. I imagine Germany, Austria and Czechia, with Munich, Salzburg and Plzen forming the 3 pillars of the map. Mountains, forests, river valleys, 3 urban areas, countryside aplenty plus autobahn. A scaled down version of this:
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Otherwise I could see something like Texas, USA. Can do coastline, densely populated areas, open desert, Houston, Dallas, Amarillo or something.