In short: VirtualBox is still probably the best option for running those IE VMs, and for cases like this Docker is not really a replacement for or competitor with solutions like VirtualBox.
$ docker run -d -p 1433:1433 --env sa_password=abc123 microsoft/mssql-server-2016-express-windowsEssentially, they have a docker-API-compatible HTTP server that runs a different set of container images. Similar to how SmartOS has a docker-API-compatible HTTP server (running on top of, essentially, a Linux emulation layer).
I haven't been following it closely so I don't know what's become of it since then, but if you want IE you're going to need that work.
For other browsers, the Selenium team maintains docker images containing all of the drivers and XVFB code to make them run. They even have a debug image with xvnc on it so you can spy on the browser if something is going wrong.
Actually Microsoft has been contributing quite a bit to the OCI (Open Container Initiative), as well as Docker. So they have been putting in the work. I'm not really partial to Microsoft, but they do have some good engineers that are working on free software.