I would like to see a feature similar to the Log4j2's ContextDataProvider:
https://logging.apache.org/log4j/2.x/manual/extending.html#:~:text=Custom%20ContextDataProvider

This would be extremely helpful for tracing and injecting trace id, span id and other tracing context information.

This would prevent bytcode-enhancements like these:

https://github.com/open-telemetry/opentelemetry-java-instrumentation/tree/0302e9b921ba1e110b8cca66293f91bf1fb13253/instrumentation/logback/logback-appender-1.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/logback/appender/v1_0

https://github.com/DataDog/dd-trace-java/tree/751f632e7bdbfb28be42638d2338088f91eda95d/dd-java-agent/instrumentation/logback-1/src/main/java/datadog/trace/instrumentation/logback