"the coroutines RFC has lasted longer than World War 1 or 2" This sounds bad, but I wonder how many features have taken this long to include in other languages

"the coroutines RFC has lasted longer than World War 1 or 2" This sounds bad, but I wonder how many features have taken this long to include in other languages. Is this really as out of step as it sounds? There is the move-fast-break-things mentality, but is that how you want to design a language? Seems like we are missing some middle ground step, where there are good features, maybe even done, and stable, but they aren't getting worked into the main language. Maybe a decision making problem.