Honestly I wish we would have had 3 new tracks for each expansion.
I didn’t really feel this need that much during HD, but since I play my games with the soundtrack playlist set to Dynamic, it can get somewhat jarring when you’re playing as an African civ and the Southeast Asian tracks play, or if you’re playing as Burgundians and you hear the very much steppe-inspired tracks that came with The Last Khans.
I know it’s too much wishful thinking to ask for them to add new tracks “retroactively” to fit the old civs, but at least for civs coming with new expansions they could consider doing it.