Windows 10 Will Soon Let You Access WSL Linux Files From Explorer, Other Improvements
Windows 10 Version 1903 will most notably allow you to access "Linux files inside of File Explorer", but it's just about accessing WSL files and not any EXT4/other Linux partitions. This will allow users to more easily copy/edit/move files belonging to WSL installations.
The "Linux files" will also be accessible from PowerShell for those preferring it to the File Explorer. Microsoft has also been improving wsl.exe so it supports new commands around importing and exporting of distributions, terminating a distribution, and other commands.
Sadly, it doesn't look like Windows 10 Build 1903 will have any changes for addressing the I/O performance bottleneck with WSL... That seems to be more of a longer-term goal due to large re-engineering that is to be required. Personally that is the main issue I have remaining with Windows Subsystem for Linux on Windows 10 and Windows Server 2019. I'm also eager to see more Linux distributions to become available on WSL, such as Clear Linux, for seeing the performance potential.
More details on these forthcoming improvements to Windows 10 WSL are spelled out at the Microsoft Command Line Blog.