It'd be nice to make use of the Java 11 versions of inflate() and deflate() so that buffers that aren't array-backed can be used.
One option would be to produce a multi-release jar with a different class for 8 and 11. That might make it so jwarc is difficult to compile correctly on 8 though.
LambdaMetaFactory might be a reasonable runtime method selection mechanism with minimal performance overhead. (example)