I'd mentioned this in #3990 (comment).

It would be nice to be able to refer in source code to newer types (e.g., CRC32C, VarHandle, and @ReservedStackAccess)—with, of course, appropriate runtime guards. Of course, that would be incompatible with one of the possible approaches to #3990, which is to use --release.

(Using Java 11 might also still dodge bugs in older versions of javac.)

We'd probably accept a PR for this unless some of our users want to tell us that they build Guava from source themselves with javac 8 (or 9 or 10), in which case the decision would get more complex.