If no one knows the who this singer is, so noted in his time for the purity of his voice and perfect pitch, my bet is that most of the singers listed above, with the possible exceptions of Sinatra, Caruso and Elvis (as a pop icon, certainly not a singer) will be as obscure at the turn of the 22nd Century as he appears to be now. If it weren't for Mendelsohn, Bach would probably be as obscure a composer as 99% of his contemporaries. I guess everything is relative to the time we live in.