Are there plans for Shotwell to have face recognition and to categorize photos according to faces?
We do have plans to add face recognition and a Faces (or People) view to Shotwell: Bugzilla - Shotwell - Face detection
There's been some movement on a patch from community contributors, but there's still plenty of work to do.
UPDATE: Adventuresome Shotwell users unafraid to run development code should read my answer to How can I compile Shotwell to be able to use the faces feature?
Shotwell version 0.29.3 is supposed to come with the face detection tool that was previously developed during Google summer of Code. I could only find this link stating this and release notes for this version was not found anywhere.