That will be the spin-off, no doubt. But people probably aren't ready for it right away -- pedophiles are still creepy.
However, people are already aware that (a) girls used to get married very young; and (b) there are 13-year old girls who could easily pass as older. It's still heterosexual, though, and thus "understandable." The only stumbling block is age difference, but as you see in the article, they're already undermining that taboo. Besides, the young girl/old guy angle would drive the whole plot line.
There's undoubtedly some of-age and stacked young thing who can pull off the role of precocious young teen girl. HBO could probably make it work, and the Supreme Court has made clear that there's nothing to stop them from trying.
I predict you'll see it within 5 years.