Able to grab libraries from crates.io and mix-and-match them with confidence, no matter what runtime or other libraries you are using
Able to easily author libraries that can be combined with other libraries and are independent of runtime
Able to easily change applications between runtimes to explore new possibilities
Able to easily author new runtimes that try out a new execution strategy or for some new environment and have them interoperate with most extant libraries, without the need to change those libraries
Able to find runtimes that fit a wide variety of scenarios and use patterns