It is already effectively thus in practical terms, sorry to disappoint you. Any time two random Europeans meet and do not speak each other’s language, the first option they’ll reach for is basic English. There are very, very few localized exceptions (some Eastern Europeans will reach for German).

That's not quite correct as stated. People usually try the local language first, if they can speak it at all. At that point they don't even know what each other's languages are. So two British people meeting for the first time in Germany may well start off by speaking German to each other. I've seen that happen a few times.

But I've also seen a German speak bad English to someone just because they looked foreign. They were foreign, but having lived in German for a while they could speak German better than they could English, and after a while they politely pointed this out. It was a bit embarrassing. It is definitely better to try the local language first.