This is a solved problem, just look at how EFF's certbot works. You cannot just claim that you are porn.com unless you put a payload there that matches what the bot expects.
And force everyone who wants to publish an extension to buy and manage a domain name? What if it expires? You're just replacing one set of problems with another.
And force everyone who wants to publish an extension to buy and manage a domain name? What if it expires? You're just replacing one set of problems with another.