The reality is that copyright law treats the author, not maintainer, as owner. Matt is the author of less than 1% of the codebase by line. To relicense, he would need consent from the remaining 99%. I'm not sure how you could argue otherwise.
Yes, if everyone signed a CLA with copyright assignment, as is common in some projects that are still nevertheless GPL, then he could relicense, but because he has not done that (and because it's actually a fork initially), he cannot relicense.
Yes, if everyone signed a CLA with copyright assignment, as is common in some projects that are still nevertheless GPL, then he could relicense, but because he has not done that (and because it's actually a fork initially), he cannot relicense.