Make writing asynchronous code easier by having a consistent way of propagating "context" across related asynchronous operations. Have the "context" be responsible for async-local-storage, allowing the execution before and after hooks, and "context"-local error handling. Finally make sure that the "context"s are composable.
This feature needs to be part of the platform so that library and framework authors can relay on a common well know API, otherwise adoption will be limited.