The susceptibility of the SD card to data corruption is a big showstopper. The only digital files I've had corrupted were stored on my phone's external SD cards (after 3 to 7 years). When I looked into it, it seemed to be an issue related to lack of radiation hardening. So if you do make this service, please include some error detection/error correction metadata.
I hope to fix up my prototype and launch it next year.
https://www.clonecamel.com/
If anyone knows of a quality source of bulk SD cards or flash drives in high capacity please let me know.