If you don't like my alternative, fine; it has its own set of tradeoffs that might be net positive or negative. If you want to proceed with the current approach, then I won't stand in the way. At the very least there should be some boilerplate added to EnumSet that makes it clear that EnumSet itself never appears in the serial form.
I don't disagree, there are many things that could be improved.
I only volunteered to bring EnumSet (as the poster child for the Serialization Proxy Pattern) into a no-worse state than other classes implementing the pattern. The doc of the writeReplace and readObject methods is pretty good implicit documentation that the pattern applies here. Serialization overall remains as deeply flawed as ever.
I still plan to submit what I have now.
Thanks for volunteering. It goes to show that no good deed goes unpunished. :-) To close the loop on this, I think what you have is acceptable. I also think that "no-worse state" is a better characterization than "Best Practice," which seems to imply that no further improvement is possible or necessary. And finally, Jon Gibbons has filed JDK-8193019 to cover future javadoc enhancements to better support serialization. s'marks