The trust store refers to the collection of parties that ultimately verify the signed claim of your control over a domain, which might have taken the form of a DNS TXT challenge (or any other number of challenges). You still need it, because there would otherwise be a basic circularity when determining whether to trust a connection.
(Moving the PKI into DNS does not remove it, it just moves it around.)
(Moving the PKI into DNS does not remove it, it just moves it around.)