Wario appeared during the Brawl reveal so I guess it makes sense to speculate a second WarioWare rep was a possibility during Brawl's speculation, however, prior to Brawl not very many people were exposed to Ashley's song so choosing which WarioWare character best fit the series after Wario was a toss up.
I think Ashley's song is what separated her from the rest of the WarioWare cast. Of all the songs (and I mean
ALL the songs not just WarioWare) that were remixed for Brawl Ashley's song was one of the more memorable. The guy who wrote Ashley's song was nothing less of a genius!
Anyone who played Brawl could instantly recognize Ashley's song by singing any one single line from the Chorus. Those lyrics have become embroidered in our heads. Because the lyrics of the song bounce back and forth between the Chorus and Ashley singing their parts you could sing any line from the Chorus and your friend would instantly know how to respond by singing Ashley's following line.
It's blatant Sakurai loves the song. Among the other WarioWare songs in Brawl that could have been brought back for Wii U/3DS he saved those Ashley songs like saving his favorite child in a house fire! Not only that but remixed a new Ashley song for the Japanese version!
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Even on the unfortunate day of Ashley's AT reveal Sakurai reveals her by singing her song. Without a doubt those Ashley songs will return for Smash Ultimate. Hopefully the other regions outside of Japan will receive the Japan exclusive Ashley song from the Wii U/3DS. Heck, a new remix of Ashley's song might be in the works for Smash Ultimate!