I guess I don't see why, if you really really need to see your image playlist, using the existing Zones system is that much of a hardship. I just tested it out and it works quite well. You can have music going on Zone 1 (and even detach the display and have a visualizer open if you want), then switch to Zone 2 and start your Image slideshow going (and use that in full screen Display View or Detached View or whatever). You still have full access to both Playing Now lists then...
It's not a hardship and it works quite well, especially when using detached view and 'always on top'.
I always look to these things from a intuitive point of view. For me this is a nice technical workaround, i can get used to. But it is not intuitive. To my opinion at least.
I always try to see a new release through the eyes of a newbe, who like to ask as little as possible questions to be able to use MC.
Cheers.