In my opinion Picasa and iPhoto as well as the new Photo App are just really bad. The worst thing about Apples Photo Apps is that they want to keep their own folder structure, but my workflow is to organize the folders in the file system and I just need a lightweight viewer to switch through the Photos after a shoot and delete the bad ones.
The key points I´m looking for are
1. display Photos in Fullscreen mode, go back and forth with the arrow keys
2. being able to delete photos by pressing backspace
3. zooming in (this should be easy for Affinity ;) )
4. see Camera Settings in Grid mode in an EXIF Panel (ISO, f-stop, exposure time..)
I would really love to have these 4 key functions!!
Please do this ;) it´s low hanging fruit!
EDIT
I´ve to add that RAW batch processing and rating systems are also desperately needed!
This makes it more difficult but you just HAVE TO do it
- otherwise AP experience is just not close to Adobe´s eco system!