Can't speak to the official introduction, but you have a workaround available by defining this protocol in your project today:
public protocol ATAsyncSequence<Element>: AsyncSequence { }
and extend whatever concrete sequence types you use to conform to ATAsyncSequence:
extension AsyncCompactMapSequence: ATAsyncSequence { }
extension AsyncFilterSequence: ATAsyncSequence { }
extension AsyncFlatMapSequence: ATAsyncSequence { }
...
Once you have that in your project you can use ATAsyncSequence wherever you needed the specificity:
func collectZeros(_ input: some ATAsyncSequence<Int>) -> some ATAsyncSequence<Int> {
return input.filter { $0 == 0 }
}