There were rumours about both X OOO and third Rider, but then he can't accept it after DecaEnd found out they were fake, and since they X OOO came from the same source probably, it is not true either.
But that means the medals are either man made or they come from a seventh greeed, and I'd be surprised if we got a movie-exclusive greeed. The man made, eh, we've seen man made cores in Movie War so we'll see. Although personally, I think the medals will just be exclusive toy combos. Honestly, given the nature of OOO so far, I'd be surprised if we get that kind of movie exclusive form. Unless this is like double and the movie is based at the very end, with the movie combo being a suped up version of the ultimate form...and I don't think a reptile form is going to be stronger than the forms we've seen so far. In fact, logically, it'd be the same as the established combos (bar Tajodor/l)
And if it's a choice of reptilian forms, bring on dinoform. If for no other reason then I want to know how the hell they got the abilities of dinosaurs into 10 core medals 800 years ago. Although I had an interesting chat today when a friend theorised Giru may have only been recently created, and might be linked to Foundation X and the Museum. Which kinda makes sense, especially the museum part. If you want to use dino powers, go to the one place in Japan you can apparently dig up a T. rex.
Dr.Maki goes to Futo!!!! Meets up with Stopwatch Lady, finds Maria, brings her Kougami, and voila, Giru. Then we can have Double come over with a crossover.
Which would be fine if OOO and Double were in the same world. But we have no direct confirmation of that, and contradicting info regarding that matter too.