Microsoft PM working on WSL & Command Line here.
WSL is primarily designed to bring one or more Linux command-line environments alongside all your favorite Windows tools. WSL runs native Linux ELF-64 binaries directly on Windows, and enables you to run your favorite Linux tools atop your Windows "host" OS, sharing the same underlying filesystem, networking, process list, etc. as the host OS.
Docker, on the other hand, provides a way to quickly & easily create a container that essentially wraps a shared (host) kernel & OS, with additional layers of extra functionality (e.g. adding Java, Ruby, MySQL, etc.). It's also easy to pcakge, deploy, and/or share your Docker containers with others if you wish.
WSL is built as a productivity tool for developers & IT Pro's who need a local, immediate, genuine Linux-compatible environment that integrates with Windows, and allows Linux tools to run alongside and/or interact with Windows files/apps.
Docker is built to enable isolated containers to be quickly, reliably, and repeatedly constructed, deployed and/or shared, but do not integrate deeply with your host machine's OS.
WSL is a local dev productivity feature, but is not suitable as a host for production workloads - that's where Docker and/or VM's shine.
To learn more about WSL, review the videos & docs here: https://aka.ms/learnwsl