I'm a fan of making Peach look as much like Daisy as possible- if we are going to go for having Daisy hinted at, I prefer to go all out and just make it an alt costume, rather than a half done visual (of which I truly do not understand the point other than potentially saving some time in development. Looking at you, Skyward Sword Link).
I think its absurd to assume Daisy could be an actual character to represent the Mario franchise without first adding in four or five other characters, because would over saturate Marios representation with princesses and females rather than quirky animals and aggressors, which is the majority of what you see when you play any given Mario game (not three princesses, two plumbers, and a turtle).
In the grand scheme of characters in smash brothers, there are far more similarities between Daisy and Peach than there are differences- yes, they have different personalities, but we are not talking about Ganondorf playing as if he were Peach- we are talking about Daisy playing as if she were.