If one imports a package that is exported with mandatory attributes the error message in the manifest should show an enhanced error message indicating that the mandatory attribute is missing and should provide a quick-fix to add the mandatory attributes with the value from the provider.

A Minimal example MANIFEST.MFs:

• Provider:

Manifest-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-SymbolicName: foo.provider
Bundle-Version: 1.0.0.qualifier
Export-Package: org.foo;attr=val;mandatory:=attr

• Consumer:

Manifest-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-SymbolicName: foo.consumer
Bundle-Version: 1.0.0.qualifier
Import-Package: org.foo

A quick-fix should change the package import to Import-Package: org.foo;attr=val.

IIRC the PDE-state provides information why a required capability failed to resolve so this hopefully reveals. If that information is not available, in case of a unresolved Import-Package we could check the state for providers of that package and see if they have mandatory attributes.
The case of multiple providers with different mandatory attributes or different attribute values should be handled too. The best would then probably be to provide a error resolution for each possible change that should fix the resolution error (maybe limiting the number of possible resolutions).