Huh, that's an interesting point. I never thought about that before, but you may be on to something there. Now that all the keyblade wielding trios have been reunited (minus Sora, but he won't be down for the count for long) there are already more than seven wielders of light. So I could very well see them intending for this to be relevant in some way.
Elrena/Larxene and Lauriam/Marluxia may also join the ranks. I don't know for sure, since Larxene didn't seem interested in repenting for her actions when she faded away, but Marluxia seemed to be admitting that he was feeling some kind of emotion, and I got the distinct sense that he was feeling guilt for his actions. There's also Luxord, who seemed to be somewhat repentant. And we all know that Demyx switched sides with Even. And we can only assume that Demyx and Luxord were keyblade wielders during the age of fairy tales, but who knows for sure at this point?
Anyways, I like this detail. You very well may be onto something.