I don't know if there's a single document somewhere with an explicit roadmap. Their GitHub page (https://github.com/Microsoft/BashOnWindows) includes links to multiple sources that could collectively be considered a sort of roadmap, including the Issue tracker, UserVoice page, team blog, and discussion forums. I've also asked the devs questions on Twitter a couple times (like @richturn_ms) and usually gotten fast responses.
Regarding roadmap, to be honest, we don't really have one, but we do have a primary mission which we're laser-focused on: Make Windows Subsystem for Linux able to run the vast majority of tools developers need to get their work done.
We've taken a somewhat unusual, but HIGHLY valuable approach of building features based almost entirely on feedback from the community. We prioritize syscall implementation based on the frequency with which we see failures due to missing, incomplete, or incorrect syscalls. This way, we focus on delivering the most bang for the buck.
This said, now that our syscall coverage is starting to edge towards covering the majority of mainstream dev tools, we're starting to look at more strategic, features including improving disk perf & support for networking, device, etc.
We'll be publishing more details in a few weeks on our blog above (and, of course via https://twitter.com/richturn_ms) on where we're going to invest effort beyond Creators Update. Look forward to hearing from y'all ;)
