I think RVD wins here. In my opinion, it would be a major step down for him, but would be a great way to clear him from any thought of being in the main event. Which in my opinion is needed. The other thing it can do is possibly give Ion a chance to have an actual feud. While, his run has been less than stellar, who has he had to feud with? No one. Kenny King was okay, but that felt rushed and didn't fit. Maybe, just maybe, losing to RVD and eventually winning it back from him will be a big step for Ion.
If not Ion, then RVD brings a instant feel of importance back to the x-division. He is a former World Champ. That is a big deal. In the past, guys like AJ have come back after world title reigns and competed for x-division titles. RVD seems like a good fit. Don't forget, also, that the x-division champ gets a shot at the world title at Destination X. In all seriousness, does anyone see Jesse Sorenson, Zema Ion, Sonjay Dutt, or any of the other people that have recently competed in the x-division headlining a PPV? NO WAY! So, TNA needs to move the title in the direction of making the title holder a realistic challenger. RVD could be that guy. Will he hold the belt that long? I doubt it, but you can instantly put him in a feud with someone who could be a challenger.
Even a guy like AJ could come out of the woodworks at the right time and jump back in the division. He certainly isn't getting a title shot any other way.