His general points about Emacs releases are pretty much still true. A
package like flycheck would be better of in something like ELPA and
bundled into an Emacs+ELPA package.
I'm having a hard time here making myself clear, it seems! I am not suggesting copyright assignment, I am not suggesting pulling the sources into the Emacs repo, I am merely suggesting shipping Flycheck with Emacs.
I'm also saying that's a good model for other third-party code like Org and CEDET.