It is nothing new for those that are classified as Bethelietes. it has always been the procedure that if you are a betheliete your judicial committee might be bethelietes. Normally it would be a brother from Service, your table head and then another elder in bethel. If you are a missionary it would be the same thing except with the home overseer of the missionary home.
It is because Bethel considers those in the Religious Order of Special Full Time Servants of Jehovah's Witnesses as being a family and that the discipline would be conducted within the family. Now construction volunteers fall within that order now.
And the letter did not say that all of those cases would be handled directly by elders in bethel but that they will choose if they are to take the case directly or let the local body of elders handle it. Also, it is important for those who are remote, that if the person is reproved or the body may choose that the investigative committee doesn't have sufficient evidence to continue, bethel may want to revoke their assignment and revoke access to their systems.