While browsing Rightstuf for figures, I spotted a Seto no Hanayome figure (Seto San) will be available next year (allegedly January 30th). Though "pricy" (about $90 US), it offers her in a sitting position; she's in her human form with school uniform, or can be configured (with costume change) in her mermaid form.
If popular enough, I suppose other related figures could be made available (though I've seen no promises or previews suggesting that's the case).
Though I'd be prefering more "cheesecake" [i.e., the other mermaids and Mawari--or should I say, "fishcake"
?] , I can easily imagine Masa would be one of the next releases, given his general popularity. If so, it will be interesting, if only because it's been a while since a "GAR-ish" character has been done as a figurine.