I have some questions; hope the OP is still around!

Will there be partial application?

    let appendHelloFile = appendFile("Hello");

    let f = openFile("log.txt");

    let f2 = appendHelloFile(f);

    closeFile(f2);

I suppose this might complicate the linear type system?

Will there be a pipeline operator? I think this fits really nicely with linear types:

    openFile("log.txt")
    |> appendFile("Hello")
    |> closeFile

This may be at odds with the no operator precedence rule.

You say that async will not be baked into the langauge. I think this is the right decision. However, will there be a syntatic sugar that can be used to avoid the "pyramid of doom" when writing promise-orientated code? It is possible to make this general purpose if done right.