As much as I love Ai Shinozaki, and would be ecstatic to see her do porn, the chances are practically zero. "Gravure idols" who go into JAV virtually always fit one or both of the following categories:
1. Idols who have done "almost-AV" (skimpy clothes like "T-back" and see-through lingerie, simulated sex, extremely suggestive and dirty actions)
2. Semi-popular idols who are kind of floundering in their careers, who can go from being a C-list idol to an A-list porn star
For an A-list gravure idol, who has never done anything more raunchy than a simple bikini shoot to go directly to porn... I don't think that has EVER happened. Not to mention that Ai has just started to cross over into mainstream gigs like variety shows. Personally I doubt she'll ever do porn, but if she did, it certainly wouldn't be any time soon.