When I play an album, it would be nice to be able to see the elapsed, and even more useful, the remaining time of the whole album - which is the same as the elapsed/remaining time for the whole playlist.

One place to display this would be the header of the playlist page.  No room for a progress bar, but just something like:

Playlist                       Total Time: 10:20/-30:40

would do the trick.

I think a progress bar at the bottom would be confusing and would waste valuable space on the playlist page, so I do NOT recommend that approach.