Reality Subtext: According to this interview, Houka's actress wanted to be MagiRed, while Kai's actor never expected to be chosen for the part. Puts the two-parter where they switch bodies into a whole new light, doesn't it?
What Could Have Been: According to this interview, Beppu Ayumi, who played Houka, tried out for the role of Magi Red, and Matsumoto Hiroya, who played Tsubasa, supported her in this. Thus, we would have gotten the first female red Ranger four years earlier.
Furthermore, there were many different mech configurations, like SeraphKaiser, a fusion of Wolzard and Unigolon, that never made it into the show.