Sneakernet updates seem doable? If you follow the "adding the quality content" link to https://github.com/iiab/iiab/wiki/IIAB-Installation#add-cont... , there are many sources mentioned, like Kiwix ZIM files, which can include fairly frequent updates.

If you are in a place without connection, how do you get updates? Any kind of diff mechanism with USB storage?

I think a hot swap system would work best. The central office of an aid organisation could just send new drives along with workers delivering food and other supplies.

I imagine you could keep it relatively up-to-date that way.