Another downside to adding one’s package to ELPA is the inconvenience.  On GitHub one can freely commit however he wants, receive PR and issues; but if it’s in ELPA, you need to take care of commit message formats, submit a patch and wait for someone to review & commit the patch.

I thought that the advantage of ELPA was that the author could develop the package independently of the strict emacs commit rules and he only had to pay attention to the copyright assignment.