True, 4KQ maintained an ageing audience while Gold 104.3 and WSFM evolved away from the Boomers and towards Gen X (although if you look at the latest ratings, Gold 104.3 has the widest appeal across all demographics of any commercial station, which perhaps says something about the appeal of 80s music.
The only music station demographically older than Gold is now Smooth, a down-tempo format. I would suggest nobody really knows what happens if you insert another station demographically older than Gold that is up-tempo. It’s also a big assumption music couldn’t work anymore at all on 1278 AM. In Adelaide, 1323 AM spent years in talk and sport (as Radio 1323, then 5DN, then SEN) before Cruise came along. The AM band in Melbourne also still hosts two of the city’s biggest stations - 3AW and ABC Radio Melbourne and the Smooth ratings indicate some of these listeners drift away from talk, especially in the PM, and listen to music.
And just because formats have been suggested here for Brisbane 882 and Melbourne 1278 doesn’t necessarily suggest Sydney 954 is suited to music. My last point was more that I think two years had been long enough to determine these three stations aren’t necessarily a matching combo and might be better to all go off in different programming directions.