Hi,
Currently using the Windows 10 IoT Core Dashboard can still only flash the iot core image for Raspberry Pi 2 or 3 devices. It must be stated that even for Raspberry Pi 3B+, you must use the 3B+ technical preview. There is currently no version support for Raspberry Pi 4.
https://learn.microsoft.com/en-us/windows/iot-core/tutorials/rpi
There was a lot of discussion on this in the forum. As for the plan you mentioned, I'm sorry, I don't know.
https://social.msdn.microsoft.com/Forums/en-US/8092f66a-2910-48dd-abd6-141c8487eec6/raspberry-pi-4-is-now-available-where-is-windows-iot?forum=WindowsIoT