Nintendo of Japan has revealed 2 new Nintendo 3DS themes: Pokémon Riding on Laplace (ポケモン ラプラスに乗って) and Pokémon Pikachu Pretending to be the Boss (ポケモン ボスごっこピカチュ) which are available to purchase on the eShop for 200yen each. Both themes are available on the Japanese Nintendo 3DS eShop as of September 19th, 2018.

Pokémon Riding on Laplace

Features: Pikachu riding on Laplace on both the top and bottom screens but with different artwork.
Music: Pocket Monsters Omega Ruby Alpha Sapphire ～Surf～ (ポケットモンスター オメガルビー・アルファサファイア』～なみのり～)

Pikachu Pretending to be the Boss

Features: Pikachu dressed as Giovanni is displayed on the top screen while artwork on Pikachu dressed as Archie, Maxie, Cyrus, Ghetsis, Lysandre and Guzma are displayed on bottom screen.
Music: Pocket Monsters Ultra Sun Ultra Moon Battle with Sakaki BGM (ポケットモンスター ウルトラサン・ウルトラムーン』～サカキとの戦闘BGM～)

Source: https://www.nintendo.co.jp/hardware/3dsseries/theme/index.html