It would actually be a natural fit to sign on a singer to the position if the show plans to delve into that part of the character’s personal history, which is really the only reason this comment isn’t completely outlandish.
While we now know Rhaegar Targaryen was a man who sparked a very bloody war in Westeros after “kidnapping” Lyanna Stark, history tells us that Rhaegar Targaryen was actually a pretty gentle dude, and one who loved to singer.
The Tower of Joy sequences have been one of the key focuses of Bran delving into the past, but we haven’t met Rhaegar, yet.