Found on 2chan by crystalsuicune. Still heavily rumored, and until official word is received, the song lists will not be updated. New songs not seen before in consoles in bold.
Taiko PSP DX is expected to have 70 songs.
・JPOP
よく遊びよく学べ (Yoku Asobi Yoku Manabe)
ヘビーローテーション (Heavy Rotation)
ありがとう (Arigatou)
I Wish For You
天体観測 (Tentai Kansoku)
紅 (Kurenai)
･バラエティ
情熱大陸 (Shounetsu Tairiku)
MISTER
･アニメ
One day(ワンピースより)
No buts!(とある魔術の禁書目録Ⅱより)
･ゲーム
モンスターハンターメドレー (Monster Hunter Medley)
The world is all one(アイドルマスター2より)
キラメキラリ(アイドルマスター2より) (Kirame Kirari)
･クラシック
第九交響曲 (Ode to Joy)
アイネクライネナハトムジーク(モーツァルト) (Eine Kleine Nachtmuzik)
練習曲Op.10-4 (Etude Op.10-4)
･ナムコオリジナル
Rotter Tarmination
らんぶる乱舞 (Rumble Ranbu)
DON'T CUT
Mulberry
ドン・エンガスの笛吹き (Don Engasu no Fuefuki)
リンダは今日も絶好調 (Rinda wa Kyou mo Zekkouchou) (don't remember this? It was only on Taiko 10, go look for it)
スポーツ・ダイジェスドン～Fill in The Sky～ (Sports Digestion ~Fill in the Sky~)
十露盤2000 (Soroban 2000)
Before you start raging at all the old songs, remember, not only is this just a rumor, but most of these are also songs that have never been on PSP before. Fan service for people who play PSP Taiko and never touched the DS/Wii Taikos. And besides, there are sure to be new songs. Remember how peeved we were at Wii3 for not having new songs, then followed by awe as bombshell after bombshell got unlocked?
Mulberry alone is worth the price of admission, in my opinion.
