I think a plumbing-level security implementation detail should be a little less intrusive than having to move either the corporate domain or millions of user's

I think a plumbing-level security implementation detail should be a little less intrusive than having to move either the corporate domain or millions of user's addresses. I can't imagine Tumblr rolling out HPKP now with this workaround (though github did do the .com -> .io thing, so who knows). The spec should've just included excludeSubDomains=