If your son is a junior and is already getting this type of interest, I would be cautiously optimistic. It certainly is too early to know whether they'll make an offer in the future, but it sounds as if they definitely want to get to know him and have him become familiar with their program. It is awesome that he is on their radar screen so early in the game!
If your son has even mild interest in this program, it probably would behoove you to make the trip. (Even if he ends up not liking the place, it will be a beneficial trip in that he will learn what he doesn't want in a school or program.) If it is a big time ACC school like you say, the program most likely will be extending offers by early next summmer -- if not even earlier. Because of this, if your son receives an offer from them, he probably won't have the opportunity to take an official visit before he is asked to give them an answer. And even if he is able to visit the school next summer, he won't be able to see what things are like during the school year when everyone is on campus.
Best wishes to your son as he starts the recruiting process!