We wrote more about it here: https://medium.com/wasmer/webassembly-cloudabi-b573047fd0a9
I firmly believe that this project is incomplete without a standard like .war (Web ARchive, from the Java ecosystem).
Of course, you could just use what's out there eg. .app (macos) or .appimage (gnu/linux) but there has to be a well-defined and clearly endorsed way of distributing wasmer'd apps.
Double so for anything exposed to the internet.
That said, the OS-sanctioned runtime could very well support a shared-object-like approach instead of one-binary-per-app but that would 1. complicate the runtime quite a lot 2. hinder startup times of wasm apps due to dependency solving.