Thanks for taking a look! I haven't used Expo, but looking at the docs I wonder if using 'allowEditing: false' and 'exif: true' in the ImagePickerOptions would bypass reencoding? The gainmap is stored in the EXIF data. Instagram is similar in that the gainmap is stripped if you edit the image at all, cropping included, but if no crops or filters are done then the image retains the gainmap.
Either way if the clients are able to render the HDR images, I think uploading on web is still a usable implementation.
I just did some more research and we probably won't do the work until there's more demand. We can actually easily support it on desktop (we upload the raw bytes but always default to serving a compressed version, which I can override for HDR) but for mobile there's no drop-in solution for Expo apps and thus would have to build 4 new things (iOS and Android uploader and display components). That said, I'd like to do this because I want PIECES to have a rich visual experience and was thinking of recruiting more photographers, but probably not now. Thanks for your interest though.
That's fair enough, thanks for taking a look into it anyway!