If I have an SD card for extra storage and tuck it away somewhere, any interruption in power would mean it needs to be manually reset. I actually wanted something with SD storage that I could turn on and off remotely.
I think the SD card is thought of as the worst tier of storage, so if you're not wanting to boot from the SD card, then the idea is to use something like a USB disk etc. Presumably, it causes more problems (bricked devices) if they don't always boot from the SD card preferentially.
One solution would be to always boot from the SD card and either have it partitioned to provide the SD storage that you want, or use the eMMC etc to provide the storage.
