I have looked at the pull requests on Github many times. I have cloned the repo to my own computer, but haven't really used that to do much. I find Github very easy to use, and (to me) it has the lowest bar to get more eyes passively looking at the code. As a security guy, I appreciate the extra time and effort that goes into signing commits and merges even if I have not personally verified the signatures. I would like to see bitcoin core continue to use github, but have no objection to additional mirrors of the repo being hosted on different sites.