I suppose “evidence that the site’s leadership has permanently changed” would convince me. Whoever decided to put in the code that causes visitors to DDOS someone should never be running a web site again.
I mean, probably not. Maybe if they posted a public apology (an actual one, not a 'I'm sorry I was caught' one), listed the steps that they would take to ensure it doesn't happen again and how the fact that they weren't doing it could be publicly verified.
They've shown they're willing to deliberately weaponize their users to fight a personal dispute with someone, and didn't take corrective action when called out. Trustworthiness is something you lose and don't get back.
And since the site stores unauthorized copies of content, I don't expect any new leadership would be willing to announce much more than a pseudonym.