Oh, he's not saying you can't by any means. He's just mentioning that there's a lot fewer people that have A) Played that one(for example, I only played the first XS) or B) Don't vote on forms that aren't specifically ranked, which XS3 Shion isn't. Nobody's saying that you can't do that, but there are people who choose not to as well.
More specifically, I even argue in favor of as many forms as I can any time I vote on a character. Part of why I was scratching my head trying to figure out a way for XS1 Albedo to beat Jecht when they met up.
Anyways, the universal status blocker thing isn't something you'll see a whole lot, though it's fine if you allow it. Not sure about the EX paths, I'd have to look back at the mechanics and such to see if I'd allow them.