That's interesting, because Matt Mullenweg, one of Wordpress's cofounders and original author, said that if he rewrote Wordpress today, he'd choose Go:
WordPress written in Go might be okay for the hosted version at WordPress.com, but it would have a lot of difficulty achieving the kind of market share that the self-hosted PHP version enjoys. I can't imagine Dreamhost et al. being happy with people recompiling WordPress Go on their platforms all the time.