You did great! One of the most interesting announcements, especially for HDR image support.

Will gain maps be supported in the future for HDR images?

To look at with chromium-based browser www.instagram.com/manuelbaboli...

I think so, if the gain map was created correctly. For example on IG the thumbnails of the last published photos (top half) in SDR are correct. Those in the lower half where I did not create the gain map correctly look washed out when viewed in SDR.