Why Observables instead of Promises?

[woutermont]

First of all: I think RxJs' Observables are amazing async streams.

However, do we or will we ever really need streams in a handler framework? I think this is perfectly possible, but just want to brainstorm a bit about use cases, because if not, simple Promises might be a leaner way to achieve all functionality.

Note that the question is not whether streams are useful in some of the applications where these handlers will also be used, but rather whether it would ever be usefull that the handlers themselves return streams rather than promises. A file stream, for example, can perfectly be returned as a promise of stream, rather than as an observable. This would seperate the handler framework from what it is used for.