Why do you want Raichu to get a Fairy type as a Mega Evolution? Some people seem to want to retcon a big chunk of previous Pokemon's types. Is that your case, TC, or you just wanted the Pika family specifically to be Fairy type?
I was actually expecting Pikachu's line to be retconned considering how they're part of the Fairy egg group. It would also make them more interesting. As for Mega Raichu being part Fairy, it would not only make it more interesting but also more useful.