In my opinion, that's a no-no. It was made a legendary Pokemon, yet it doesn't evolve into it's parent's kind (I'm not saying it should). Besides, Heart Swap was only meant for Manaphy and other Pokemon that may learn it, NOT the wannabe legendary. What use is it going to make of it? It'd still be a weak Pokemon and therefore wouldn't be used for battles so it has no point. Plus it would probably be banned in contests or ANYTHING on a side quest (Yes, I'm talking about you, Sinnoh, YOU SUCK). In the end, Phione should not be able to do something THAT silly for it's place.