That would be viable, if it would be available on gog at the steam release date (or soon enough), i would get it there but i kinda doubt it as i just looked it up and the german gog doesnt show any signs of summer's gone so far.I think you'll still be able to get it via Epic or Gog if you're in Germany. The page isn't geoblocked on Epic at least for now, I imagine Gog will be the same. They'll happy hoover up sales that Steam's unwilling to make possible.
I will not install epic just to have summers gone as my only epic launcher game