Can we See the lwc Module?

Edit (2019-05-30): LWC is now open source!

Our intent is to open source LWC by the end of the year but it will ultimately come down to resourcing constraints because there's still a lot of work to do!

There's not too much going on in the lwc module. There's basically LightningElement which exposes an API subset of HTMLElement (what we consider the "good parts"). There are also the various decorators (api, track, readonly, wire) and several other APIs that are only usable by our compiler.

To answer your question though, a single file would be the simplest type of module, but a module can contain multiple files since we are able to import and export in the same file. You can event do that with a single line using module redirects.