Never gonna happen. They haven't released anything "Stadium," related since Battle Revolution for the Wii, which was only compatible with D/P/P games. B/W/B2/W2 didn't even get it's own "stadium" related game. And considering all the Pokemon games have been 3D since X/Y, not to mention we're no longer in a day and age where people are still using transfer/game packs to use their own pokemon to play other people, I don't think there's a point into making any "stadium" related game unless they go with the "original story" route like they did with Gale Of Darkness for the GameCube.
Also those games were developed by other companies (HAL & Genius Sonority Inc.). If they gave another company the go-ahead to develop another "stadium" game, it would have to be a company that would put in the same amount of effort as current-year GameFreak. Stadium through Battle Revolution had so many animations for different moves and the pokemon themselves were more animated and had an actual fucking personality. GameFreak would NEVER approve of that shit in this day and age.