If you boot any of the mainline kernel "box" images, the contents of emmc can be backed up with 'dd' but this is slow and requires an SD card (or USB) larger than the emmc size to store the image. At least with S905 devices the emmc sizes are typically 8-16GB only so that's not such a big deal.
NB: LE does not support update of legacy OS installs to the LE10 codebase, a clean install is required. If the Amlogic 3.14 kernel is detected during update we abort, and if you manually override the compat check the box will (guaranteed 100%) end up in a broken boot state.