You’ll need to use the Media Browser to re-add the photos in RW6 - or, open iPhoto and then RW5. We’ve heard reports that your albums will appear. At which point, save your document - and open the RW5 document in RW6.
We moved away from Albums last year with RW 6 for a number of reasons (namely: the iPhoto/Aperture -> Photos move, the fact that not everyone uses iPhoto, and the change to being a sandboxed app meant that the location of images was not guaranteed to be accessible). We’re not planning to tie to albums in the future, but we are looking at expanding the sources available in the Media Browser
@nikf – Can you tie to ‘Collections’ in Adobe Lightroom? I think that is THE most popular photo app on the market for storing, cataloguing, correcting, publishing, etc…