Would it be possible to prepare dual or triple system SD card?
I know that with Android it would be little problematic, but other Linux based systems usually have separate partition for boot loader/kernel and second one for real OS. This bootloader partition could be common for for example Ubuntu, Armbian and OpenELEC for example.
Usually typical 16GB SD cards are almost empty, it would be nice to have 2-3 systems on one card.
I believe so. This has been discussed somewhere in the forum, but I do not have the link to it now. Basically you need to have a cmdline.txt file in you boot partition, and it must contain root=/dev/sdXn, Xn being something like a1, i.e. sda1, or sdb3, etc. You will need to edit your /etc/fstab file too. This is something I want to try, just haven't had the time yet. Please post here your results if you get the chance to try this.
I think this would be a nice idea.
Especially when the board is in a box with difficult access to the SD card.
And also for a single OPI+ I have no less than 7 SDcards