with commit
https://github.com/qos-ch/slf4j/commit/2d3c03622eac8b6d806203ae8eaf2732c3e2e68e
you added an OSGi Requirement

and with this an Capability for `slf4j-jdk14`
https://github.com/qos-ch/slf4j/blob/e540299d58bc5f53cab3236cc1b2f29281982074/slf4j-jdk14/src/main/resources/META-INF/MANIFEST.MF#L13

both helps so let ServiceLoader-lookup work with OSGi.

The PR https://github.com/qos-ch/slf4j/pull/321 now provides Capability for every implementation.

The inclusion of a version range in the existing requirement filters is also a definite improvement.