I’m not entirely convinced that tools would benefit much from .mod compatibility itself. Even if they were standardized in some way, they would still be tightly coupled to compiler internals, which limits their usefulness outside the build process.
Where I do see a clearer structural issue is at the ABI layer rather than the module layer. But even there, most practical interoperability needs are already covered via bind(C). So I tend to see .mod compatibility as less central than it might first appear in terms of ecosystem interoperability. These are just a build system friction point.