There are artists with tens of millions of listeners who I think will be relatively unknown in 50 years. Unless they have a song with like over a billion streams, they won't be too well known.
Look at a top billboard chart from 50 years ago, 1973 #12 is Clint Holmes. He has 7k monthly listeners now.
Look at the billboard chart for this year. #12 is Chris Brown.
Clint Holmes was roughly the Chris Brown of his day, but now he's a nobody.
I think the only people who will still be widely known are those who made a change to the music landscape, and those who were part of the wave they made.
T-Pain and Kanye with auto tune for example.
But idk, cause a lot of old artists are known for making pop hit after pop hit, so who can say.