I also find it hard to believe that humans of any sort would hold special interest to a superintelligence. Do I really have the burden of proof there?
It's plausible, to me, that a superintelligence built by humans and intended by them to care about humans would in fact care about humans, even if it didn't have the precise goals they intended it to have.
This is overly complex. Now we assume that AI goes wrong? These people want to be in a simulation; they need a Schelling point with other humanities. Why wouldn't they just give clear instructions to the AI to simulate other Earths?
A self-modifying AI is built to serve humanity. The builders know, of course, that this is much riskier than it seems, because its success would render their own observations extremely rare. To solve the problem, they direct the AI to create billions of simulated humanities in the hope that this will serve as a Schelling point to them, and make their own universe almost certainly simulated.
Plausible?