According to a trailer at TV Tokyo, it appears that Stereopony will be in the episode of Pokemon Smash! that airs this coming Christmas. Watch the trailer here. Below is a description of the episode and a translation made by ButterflySparkle.
Description
▽「ポケモンおせちを作ろう&新エンディング曲生ライブ!」
お正月に欠かせない”おせち料理”をポケスマバージョンにすると・・・ピカチュ
ウやダルマッカ、ムンナなど、おめでたいポケモンでいっぱいに!
▽ステレオポニーとガチバトル!
Translation
Make Pokemon New year’s Food and a New Ending Song Live!
The missing “New year’s food” is made in Pokesuma* version …. Pikachu or
Darumaka, Munna, etc..make tons of special food!
Music Battle with Stereopony!