Theoretically you can move disk between RPi3 and 4. This should not be an issue. However the RPi5 requires new firmware package which we need to implement first. There are some significant changed done by RPi developer and as of now, we are not supporting RPI5. However we will provide a dedicated image soon. On a later stage, we are thinking on an option where you can select RPi versions you like to support and our installer will download and installer required kernel packages to be able to move between different RPi version.
At the end you will be able to move within RPI family only. It will not be possible to move between RPi and RockPi or OrangePi. This is because of the kernel packages required by each board. DietPi is not an own operating system, it’s a set of bash script on top of different Debian, Raspbian or Armbian images. Each SBC has different dependency between kernel, overlay and other packages as each SBC has different CPU type and hardware components.