Game Informer is said to have exclusive behind-the-scenes information regarding Pokémon and its history, how GameFREAK brings Pokémon to life, etc. We don't know if this information will have anything from the upcoming Ultra Sun and Ultra Moon and the eventual Pokémon for Switch (even if that ends up spinoff). All I can say is stay tuned and if you already know of Pokémon's history, there could be some tidbits we haven't heard before.
EDIT - Whoop. Apparently missed this:
The eventual Pokémon for Switch did get brought up.
Masuda explains the process about Pokémon creation (the critters, not the actual games =P ). A link to the full interview can be found on GoNintendo's link above.
An excerpt from said interview:
Coming from a Game Informer interview with Game Freak's Junichi Masuda...
“The graphic designers are obviously going to be the ones finalizing the look, but it’s not just the graphic designers who come up with ideas or draw the Pokémon. These ideas come from a lot of different places, the gameplay, the visuals, the story, and in the end those ideas just get centralized and designed.
One thing we always really pay attention to is treating them like living creatures so you have to try and imagine where it would live in the environment and why it looks the way it does, what would it eat? When designing Pokémon, and not just from a graphic design perspective, there must be a reason for why it looks the way it does and you have to think about why it might live in the Pokémon world.”
"After Gold and Silver came out, it was a huge hit around the world, but shortly after everyone was saying, 'That’s it. The Pokémon fad is over! It’s dead!' It was a very stressful project, for sure. When we were first developing it, I had the idea in mind that it would be Ruby and Sapphire, and then the next games, including the titles, would be Diamond and Pearl, and in between we would do the remakes, FireRed and LeafGreen, so we could create this structure where you could take the Pokémon from the Kanto region to the Diamond and Pearl games.
At the time, the atmosphere and general thinking was that the Pokémon fad was over and there was huge pressure to prove people wrong. I got really stressed out and had to go to the hospital and had some stomach issues and had to get a camera inserted and they didn’t know what it was – very stressful. The night before release I had a dream that it was a complete failure, a total nightmare."
We at Game Freak took that as a challenge and said, 'It’s not dead. We’re going to show you guys you’re wrong!' The morning after, the day of release, I went into the local shop and saw people lining up to buy it and was extremely relieved. It was close. Super scary at the time."
*This rule basically states that you can recycle content once a certain amount of time passes. That's what GameFREAK did. They recycled so much for Gens IV and V not caring if the older Gen I and II fans seen and did it all before (Gen III was like a red flag of things to come in Gen IV and V).
In the realm of Pokemon spin-offs, some of the devs share their favorites and also share what games they wish they could make.
Coming from Junichi Masuda...
"Pokémon Go! I am not sure if you can call that a spin-off title. Pokémon Go is experiencing something similar where people are saying, ‘Eh, it’s done. The fad’s over,’ but it was way worse than that after Gold and Silver had settled down and we were working on the next game."
Coming from director Shigeru Ohmori...
"I played a lot of Pokémon Snap. I got really into it. The most fun part for me – this may have been a Japan-only thing – but you could take your game to a convenience store and print out the photos you took and could use them like stickers and put them on things. I just had a lot of fun being able to take the photos in the game and print them out as things that I could use."
Masuda and Ohmori also shared spin-off ideas they'd like to create at some point.
First up was Masuda...
"It’s kind of an Easter Egg from X and Y, but Rhydon Racing was a thing in that world. There might be a message in there that I really want to create Rhydon racing."
Followed by Ohmori...
"I really want to try working on a real action-focused game. Of course, we’ve kind of got those already with fighting games as well so it’s hard to say what it would be. Like a 2D side-scrolling action game, maybe."
Game Informer asked why Pikachu ended up so popular/the face of the franchise. GameFREAK's answer: The anime with Ash & Pikachu, duh!
Though GameFREAK admits they weren't sure how the anime would go when the anime producers asked Ikue Ōtani to do an audition for Pikachu's voice (remember Pokemon can only say their names; or growl; in the anime). But it all worked out: Pokemon became a cash-cow franchise and Ikue Ōtani cemented her role as Pikachu and continues voicing Pikachu to this day.
Masuda explains why there was no third version to Black & White (remember we got Black & White 2 instead). Apparently based on the B&W theme (yin-yang, good/evil, black & white), any Pokemon Grey would have contradicted the theme set in Black & White 1. So they ended up making Black & White 2 instead.