At the time, Nintendo's Touch! Generations line (featuring games like Brain Training) was incredibly popular. With the belief this "trend would continue", Sakurai decided he wanted to take this concept to the next level and provide a more thorough experience.
"The original plan was based on a new hardware, the 3DS, that was coming. At the time Touch! Generations was popular on DS. Touch! Generations is a general term for small software games like Brain Training. They were different from ordinary games but they gave you many benefits and were good for short periods of play...I thought the trend would continue. So I wanted to make something that will allow you to play games thoroughly, that's how I planned Kid Icarus: Uprising."
Before Kid Icarus was even in the picture, the framework for this more substantial take on the Touch! Generations series had been laid out. The plan was to make a third-person shooter, but due to the size of the 3DS screen and limits of the 3D, person-to-person battles weren't really going to cut it. And so in Kid Icarus: Uprising we see Pit taking on giant monsters and Gods.
"We were going to make a third-person shooter because the 3DS had a depth feature. But the screen is small so the depth was limited too. That's why we didn't make it a battle between a person and a person. We made the opponents many times bigger."
The game obviously turned out to be a hit and ever since there have been ongoing requests for more new entries in the series. In the very same episode of Harada's Bar, it was noted how many fans of Sakurai asked a lot about Kid Icarus: Uprising when the show was taking questions to pass on to Sakurai.
Despite how many fans would like to see this series return, earlier this year, Masahiro Sakurai mentioned how a sequel to Uprising would be difficult, which basically means it won't be happening any time soon.
And right now, of course, Sakurai is hard at work on the final DLC fighter for Super Smash Bros. Ultimate.