mysidia11
When authors sign up for an account on the new site: have the signup process provide the user a "hash code" to insert anywhere they want into the HTML code or as a HTML comment or header on their homepage to confirm author access to the plugin page on the new site.
Matt may be able to fork plugins, but they won't be able to fork every single plugin in the directory, as it isn't very feasible.
It also would then not necessarily be obvious to Matt which plugin listings in the new directory have been claimed, and which plugins are being updated by other people from the community.
I don't think there's been an Antitrust complaint against Twitch though -- this complaint would have to be formally raised by a competing streaming platform though, unfortunately. It is not enough that it harms creators or consumers (Consumers cannot raise the antitrust issue -- due to quirks in the US law; it is only competing companies such as Youtube, Trovo, etc, whose competition would be harmed by their actions or the US government who can have standing to raise an antitrust complaint - Antitrust violations and anticompetitive behavior harm consumers and other companies indirectly but the courts only give standing to sue to the actual competitors).