I think the idea of a MPG Superion could be a safe bet for another combiner in the new MPG line because of the shared engineering between the smaller bots (the limb aerialbots share similar transformations) allowing for ease of designing Scramble City style interchangable limbs (even better if the hands and feet are seperate pieces with only the torso bot having perfect transformation). I think an MPG Superion might be a good toy for TakaraTomy to test out ideas first before working on more complex combiners like Devastator.
Eh, I don't know. Let's face it, MPG Raiden *is* CHUG Raiden. They can say whatever they want, but it was made to scale with CHUG and it does that. We already have "Legacy" Superion and Bruticus coming, along with SS86 Devastator. I don't think there's a need, let alone room, for the MPG version of any of these combiners. I think Raiden was a one-off because of the strict requirements to get licensing from the train manufacturers for the alt-modes from what I heard last. (Been a while, I might be a tad fuzzy on those last details, but it was something akin to that. The licensing being a cost factor, I mean.) And honestly, between Zeta and FansToys, Superion is pretty much covered. Takara-Tomy wouldn't really be adding much to the combiner scene with the MPG version of it. Especially if it's not MP-scale.
I was hoping he would be the next combiner but rumor has it, it's probably going to be a Defensor. Superion is probably my favorite Autobot combiner. Although FT looks good, I dont' really care for the bots, they felt kind of "okay" 5 years ago to me, I could only imagine what they feel like now. Sounds like it won't be a while till they get around to him, unless something gets done in the Adamas Machina line.