Yes, I guess I should add something like this to bootmenu.sh. I was trying to find it in kernel sources and I would rather try to fix this bug in kernel so the names are consistent but it can be done as a temporary workaround. And also having such variables could be useful so one does not need to remeber naming of the slots for various devices. I'll try to add it but I'll try to figure out slot naming from information in /sys/devices/platform/mmc...

But still this bug needs to be fixed. Once you boot from such mismatched device the system device naming is not consistent. With N800 it happens when you only have card in external slot, with N810 in internal slot. Sadly with N810 this is more likely. See output of df after you boot, you may see two partitions mounted from same card but one starting with mmcblk0 and the other with mmcblk1. This may be confusing to some (system) programs and even dangerous. Imagine e.g. formatting external card in file manager and having the other card erased by mistake. Also the usb storage functionality may be confused when trying to unmount the card when you insert usb cable.