I'm not much into this thing of just uploading pictures, but I guess I would like to work into turning your Tumbless into a more full-featured static-website solution for non-devs, that works from the browser.
https://github.com/ChrisZieba/dodgercms
Regardless, I think this is something that would be awesome to have. You can even throw in some AWS Lambda if you want to move some stuff out of the browser(like generating thumbnails/index pages/etc). Or just use Lambda to run a complete static site generator(like jekyll or pelican) every time the content in an S3 bucket changes.
Note: I've never actually used either of these, but I did spend a fair amount of time researching this type of stuff.
I'm not very happy either with the hidden file approach, as it might be vulnerable to brute force attack. Amazon does not specify what kind of protection they have in place. I definitely recommend hard to guess passwords.
Now I don't know if Tumbless does everything client-side too. I guess the other way is way too hard (recompiling everything every time, finding what to recompile etc.), like I tried to do and failed with https://github.com/fiatjaf/coisas