You are correct - seems that Apple has removed cover flow from the file open dialogue. A few pointers. First - if you do NOT change the view - cover flow is there when you first execute the file open dialogue procedure. If you change the view - i.e.: icon view - it goes away - never to return. I have replicated this on a number of my OS X machines. So - don't change the view. Second - here is a workaround - while NOT cover flow - it allows you to change the icon sizing in the file open dialogue procedure. This cannot be changed via menus and must be done by dropping into terminal.
/usr/libexec/PlistBuddy -c 'set FK_DefaultIconViewSettings:iconSize 220’ ~/Library/Preferences/com.apple.finder.plist
Copy and paste the above after executing terminal. This allows you to at least see images larger than standard icon view when uploading.
I suspect cover flow is fading away after the lawsuit Apple was faced with for copyright infringement. Google to find more on that.
Strangely enough - cover flow still exists in El Cap for file browsing - but has gone away for the open dialogue proc. Maybe it was an oversight - perhaps a deliberate release 'functionality'.... Hopefully we see the return in the next maintenance release.
When uploading a file, for example attaching a file in Mail, the finder-type Open Dialog does not allow files to be viewed in Cover Flow View, as in previous versions of OS X.
Is there any way round this or has cover flow now been dropped for the file upload window?
Cover Flow View works fine in normal Finder windows.