I disagree with most statements in your last point, but I agree that we need to find a solution. Let's go point-by-point again.
A) There are no existing disabled routing solutions: That's just factually incorrect. Here's a really nice one: http://www.rollstuhlrouting.de/
B) You're breaking the map: No, I'm not. It's not like I'm disconnecting streets here or anything. It's also not like people are using a completely foreign tag that's never been heard of. We're mapping features consistently with a tag that was approved 6 years ago! If your renderer of choice is not taking that tag into account properly, let them know. They've had 6 years to figure out how to deal with it. Just see how they deal with Toronto. Sidewalks are represented everywhere like that in downtown toronto and I don't see a big problem.
C) No, it's not "my" responsibility. The tagging scheme is approved, has been approved for a long time. That sidewalk representation scheme is used in similar environments. Is it perfect? Not yet, so what? Routers and renderers need to deal with the data. Again, 6 years since that tag has been approved. It's not like it's a big shock to the community that this tag exists.