Spammers can just create a GitHub project, put the nip05 verification there as a GitHub Page and be valid for free. So, I don't really thing this does much. 

All they need is a free hosting service. They can even use their own personal computer at home behind a Tor connection to serve as the NIP05 address. 

They can even use Orbot and get their phones to reply to the nip05 verification.