Heart somewhat resembles Crys, what with the hairstyle, shorts, etc. Perhaps, if Crystal is ever remade, that Heart will get a costume to make her look like Crys. Just an idea. For one thing, every time a third sister game is made, the protagonists get costume revamps, so if a Crystal remake should ever happen (apologies, i know that's a dumb thing to speculate at this moment in time), it's possible that it will be revealed that Heart is in fact Crys. Although i really don't care less- i now love Heart, she really suits the Johto Region, with her new-age farm-girl attire. For some reason i imagine her having a Miltank on her team (when she is a supporting character in the game).
I'm really looking forward to seeing Heart's overworld sprite- I'm even considering choosing her as a character for my first playthrough.
Ok, that last one was a lie, but i'm definately going to play as her at some point. =3