Out of interest, how did you approach disk encryption? That would be my concern with removable storage. The other thing I'm keeping an eye on is Arm's LittleFS for storage longevity.
LittleFS (recently posted here) is indeed interesting, although from the documentation I couldn't figure out
1) if it works for larger devices as it seems it seems mostly intended for sizes of a few MB. I might be totally wrong with that.
2) if/how it handles corruption of complete blocks(?) of SD memory. As far as I understand, an SD card doesn't necessarily use 4K block sizes and corruption might hit multiple blocks at once. If LittleFS stores both previous and next version next to each other, I don't think that'll help in that case.
Yes with 1) I'm not sure either but there's some sporadic discussion in the Github issues with various attempts. From what I remember certain scenarios currently cause all blocks to be re-scanned which will obviously get slower with capacity.
With regards 2), I was under the impression each block is allocated according to the wear-levelling algo[0] so I don't think they're contiguous if that's what you mean. Also block size is configurable.
I tried implementing LittleFS on a 32MB SFDP flash with Mbed but couldn't get any decent performance out of it. It kept spewing out "bad block" errors an re-allocating everything. I hope it's a more viable option in future though as I do like the design.
[0] https://github.com/ARMmbed/littlefs/blob/master/DESIGN.md
Personally I want to use it as an internal filesystem for various projects (like games - instead of zip/pak files, which are really read only)
even littlefs over https might be an interesting naval gazing project :D