Questions:
1. To the extent reprocessing is necessary, will that be done automatically (e.g. as it is for photos originally uploaded at full resolution, and now being displayed at 5K)?
2. Do all mobile OSs provide the color profile management necessary for the app to properly display photos? I know this was a challenge in the past.
3. Will there be any indication a photo is outside of sRGB, aside from EXIF?
P.S. - I'm sure you're aware, but there's a (closed) group of alpha/beta users (https://www.flickr.com/groups/flickrbeta/) always eager to help provide feedback.