blocks that can change gravity

I'm not sure how technically difficult it would be to implement, but I think it would be extremely fun to add a block/slab/stair type that alters the gravity of the player (and perhaps even that of other entities/mobs). Maybe this is wishful thinking and would be too much of a balance issue for survival, but to put it simply I think it would be so cool to be able to build structures where you can walk upside down or on walls, perhaps even after a transitional screen/player animation to signify the gravitational shift. Creativity has always been at the forefront of Minecraft's identity as a game, and I would love to see this pushed to new levels with a feature like this. I could see it being balanced by having the gravity shifts only be possible within a close radius of the block, or perhaps only functional in other dimensions (specifically the end/the sift) to encourage more surreal building in those areas. Anyways, this was just a cool idea I had that I wanted to share!