Hi,
I had a look at this topic multiple times in the past and always have got the impression that there is a strong requirement on a change of JDT model API to support 1 module-info per source folder or PackageFragmentRoot (instead of 1 module-info per JavaProject as it is be the case right now). This is basically a re-spawn of the src vs test classpath issue, or more generally about the recurring issue a single project-level classpath/modulepath/module-info/... doesn't match current use-cases well.
We already discussed with the community of possible things to try in JDT to improve it, basically extracting an interface out of IJavaProject for something like ClassPathAndModuleAwareJavaElementConfiguration and get the various IJavaElement capable of returning such a configuration (usually defaulting to project's one, sometimes not). While there was some theorical good feedback on this proposal, it was never turned into action so far. The closest thiing that happened was the test classpath separation which is much more limited.
Our team at Red Hat might try to contribute something there in the future, but at the moment, our focus and workforce is almost entirely dedicated to JDT with Javac; until it reaches industrial quality and becomes default in JDT-LS, so don't expect contribution from us on this topic soon. As long as it is the case (at least until early 2025), I personally prefer skipping vague discussions; but I would react to PRs and concrete issue reports if I can be relevant.
Cheers,
