The initial and unset CSS wide values are already in development in Microsoft Edge. The all shorthand property is now on the backlog with a priority of medium. You can track status updates at https://dev.modern.ie/platform/status/cssallshorthand/
The CSS image-set() function is now on the Microsoft Edge backlog with a priority of medium. Status updates can be tracked at https://dev.modern.ie/platform/status/cssimageset
This work is now in Microsoft Edge Insiders Preview 17074 and higher.