I think I've made the comment wanting for something like this before.

I've seen the code for the way that collision functions on the map, where basically the visual and collision foo that maps do is pretty much the same thing. searches for collisions hunt through all objects on the map, causing some major speed problems when you have a lot of pure-visual objects hanging around.

While I'm not sure I'd want them to do anything more than not be involved in the collision searches at all built-in, there's definitely something to be said for having a purely-visual, visible-to-all object that hangs out on the map and doesn't trigger any of the collision-related functions.

I would hope that such objects would have a way to also act as proper global images so they can take advantage of KEEP_TOGETHER shenanigans. That might be a different feature request though so I'm not going to really push it.

As for when you might want to do a visual-only effect like this, particle effects are the first thing that comes to mind, although anytime you'd want to special effects in general clearly shouldn't be physical. Such systems will probably still run into the same issues physical objects do when it comes to animate() costs, so I doubt they're really going to be that helpful if they just skip Cross/Uncross/Bump checks.