I'm honored to be on the honorary list of a cappella your honors.
Years ago, Jessika Diamond did the research, and we both came up with some names of a larger "A Cappella Hall of Fame"
If you narrowed down the a cappella community to the "RARB-centered world" then your list is appropriate. If you were to consider the larger a cappella world then some justices would have to be bumped for the likes of...
Gene Puerling (whaddaya mean, who?)
Ysaye Barnwell & Dr. Bernice Johnson Reagon (Sweet Honey)
Jim Clancy (Vocal Majority)
Anders Jalkeus (Real Group)
Richard Greene (The Bobs)
Keith Lancaster (Acappella)
Ah well, I'm too young to be on the Supreme Court now anyways... and old enough that my college a cappella LP (that vinyl thing) is being made into a CD for my 25th reunion this May: