Rush can't here music that he can't remember before his hearing loss.
So Inviting Rihanna (not that he would) wouldn't work for him.
Elton John's music he remembers and has a big enough portfoilio of music from his younger days that as "A Wedding Band" their will be slow stuff and rock and roll for the young and geezers alike to shake their booty's too :-)....
I can't think of an old rocker that he can still hear with his implant that has all Elton has to offer. Think about it, Frankie Valley etc etc who would you have that could top Sir Elton that is more mainstream?
At least if Rush had Frankie Valle, he could have gotten onstage and performed "My Hands Explored You" with him.