This is interesting!
I feel intuitively that the levels should contain no information that cannot be gleaned from sound-based interaction, even if it makes them uglier. For instance, the only way to infer a stopper is to fail to push a crate on to a space where it is possible to walk. But there are stoppers in the revealed level 8 that cannot be verified this way because their purpose is aesthetic and there's no way to get a crate near them.
I'd also like to see levels that are designed to play with the practicalities of unsighted solving. Whether that's mechanics that involve some type of predictable disorientation (teleports, switches that open doors, holes into which you can push crates, etc) or just elements of level design that are hard to grok unsighted — something as simple as crates arranged in a plus shape, which requires some movement-based deduction.