If it were to happen, I think songs would fundamentally work differently. For example, you could only play two songs a minute, but it lasts say 30 secs. Maybe you no longer have the -25% DMG reduction but different songs consume different amounts of MP.

As for different songs besides the TP/MP song they could have skill/spell speed % like the NIN one, DEF/M.DEF+, maybe even add single target songs that increase STR/VIT/INT/etc.