Yeah, std can never break backwards compatibility. So any big thing that gets added needs to be sure it wont ever change. Something like tokio is far too large for that and already does not fit all use cases.

What I want to see is more support for interop between the different run times by providing standard interfaces for things between the various runtimes. For instance being able to spawn a task in for the runtime to take care of. You cannot do that without knowing which runtime you are using ATM. Which is highly anoying for developing libraries that need to do this. And that is only one of the many problems that could be solved in the std lib without needing to bring in the whole runtime - just create common interfaces we can use that can be implemented by each runtime,