CKDK regularly DXes (or used to before Windsor's Espace Musique station came on at 103.9) into the northern suburbs of Detroit, and I heard it frequently while growing up near Mt. Clemens, MI in the '90s. Another K104 liner I remember from that time is "K104 on the 401."
I wonder if this change was made in response to 97.5's flipping to more of a Hot AC sound? (Which it appears the other EZ Rock stations have followed suit... including 100.5 in the Sault, which I noted on a recent trip, and 105.3 in Sudbury, which I managed to hear while crossing the Mackinac Bridge - may be old news, but it was news to me.)
The idea sounds somewhat similar to the U.S. "Rewind" stations in markets like Chicago and Cincinnati. It also reminds me of when 93.9 FM in Windsor was known as "More 94" (briefly dropping the heritage CKLW-FM calls for CKMR) briefly around 1988-1990.