They say in the post that they are open for Rust team members to discuss this. So the "insiders" would be Rust team members, I think there would be some hundred

They say in the post that they are open for Rust team members to discuss this. So the "insiders" would be Rust team members, I think there would be some hundreds of people. (There are multiple Rust teams, not just Core and Moderation.) Together, they also would have considerable power over the Core team, as the teams have some power in a do-o-cracy sense of the word.