Here is something that bugs the hell out of me…
Wherever you are in the world ATC has an American accent. I don’t think it would be that hard to put in a few different English language accents in the system. Hell, my Garmin GPS could do that in the car 15 years ago - a voice synth with a British accent, Australian, even Beavis and Butthead.
Ideally, you would have English with Slavic, Indian, and Hispanic accents, and let’s say Queen’s English for the rest of the world outside of North America. It would help the immersion experience a lot I think.