Definitely, the work you've already done is a huge improvement! Symbols on Linux or Windows being less readily available in debug builds is a bigger problem, I think, that also affects the quality of things like backtraces in error reports. It's worth improving for sure, but I don't think we need to address it specifically for what you've done for key paths.
Keep in mind that the output isn't stable even on macOS, so writing tests that rely on the output being a certain way, without also having mechanisms to require reflectability of the types, properties, and other declarations involved, is not a good idea. If a test is testing debug output specifically, you could use regexes in lit like {{bar|<fallback output>}} to match either form of output. Code that is testing whether a key path refers to certain properties should continue to use the key path == operator to do so.