The Rhedosaurus COULD happen for a number of reasons:
1. It's an OLD US property - acquiring the rights would prob. be easy/inexpensive.
2. A LOT of people would buy it, in the US AND Japan!
3. 'King Kong' was the original seed of the idea for Godzilla, way back when. But 'Beast from 20,000 Fathoms' was released the year prior to 'Godzilla', & is acknowledged as the direct inspiration for Big G's look, by Tsuburaya & others who worked on the film. The historical connection between Big G & Rhedosaurus is undeniable, & I'm sure Bandai is aware of this.
I reiterate- if Tamashii has never went for US properties before in the much more popular lines like Robot Damashii or Figurarts, they aren't going to do it over Godzilla, especially since they haven't expanded the line or hinted at anything since November last year.. They had never taken the plunge before and basically sat back and let Revoltech and Figma do all the Western props (including some far more popular than Rhedosaurus) despite Bandai being the most powerful toy company in Japan. And Bandai's a corporation, I seriously doubt it will take into consideration whatever historical significance Rhedosaurus has. Bandai isn;t some sentimental love letter like M1 or something.