I would love to see the current Photo viewing slideshow option enhanced/replaced with a more sophisticated background slideshow.
The intent is really to make the slideshow a visually appealing piece to just leave on in the background (e.g. a variety of nice transitions - not talking about fade, slide, rotate, etc.)
A friend of mine had appleTV which has this very nice picture viewer mode where family photos were being cycled through almost like a scrapbook photo album. Sometimes one picture sometimes two, and on top of different background layouts and nice animations between the photo's cycling.
(tried to Google it, not sure if it was built into appleTV or an add-on, if I find out will update, hopefully with screenshots).
For those of us in the family way, this would be a really awesome addition to get personal pics running all the time, basically treating the TV as a big digital photo frame.
Additional plus's would be controls around filtering and picking different sets of photos quickly and easily.
There is so much finesse in Plex around Videos and the amazing complexity that goes with them, it would really be nice to nail the relatively much simpler picture viewing media aspect and be done with it ;-)