Hi again, I just finished The Lost Hero and came up with wacky ideas of The Son of Neptune:
First, there is an analogy.
Maybe Jason Grace is the best camper of the Roman Camp Half-Blood.
Percy is the best on the original Camp Half-Blood.
Juno said there is an exchange between them. Probably the son of Neptune is Percy as the son of Jupiter is Jason.
Next, they both lost memories. They probably both had dreams about their past. And Hera/Juno will not give back their memories. Jason started dreaming about his friends in his camp and he remembered a girl named Reyna. Maybe she is the "girlfriend" of Jason in his camp. That will make Piper insane. (*sobs for Pipes*) And because of that, maybe Percy also forgot that he has his own girlfriend at camp. Snap, that would be gruesome. Our friend Pipes may also have a counter part at the Roman camp, that will be the "couple" of Percy as Jason to Piper.
I wish the amnesia part will not happen to Percy, because that will totally twist his relationship to Annabeth. But all of these theories are just theories, and we will get the real news when The Son of Neptune arrives.
See 'ya later, folks! =]
-Sol, Son of Apollo