This is indeed sad news. When I first became involved with Mailman, Tokio was the primary maintainer of the 2.1 branch. He was very knowledgeable about Mailman and very helpful. In particular, he knew many idiosyncrasies of Japanese MUAs and the messages they produced and was very helpful in vetting changes that might affect them. More recently, Tokio was primarily involved with things other than Mailman, but he continued to make helpful contributions. I am sorry he is gone.