Small update on my note about Manabu Kusunoki being at Arzest or not, this I found may be the closest to a confirmation that he is:
http://www13.atwiki.jp/game_staff/pages/475.html
If you look at the bottom, it says in the Terra Battle credit (he made 2 characters for it after 500k downloads I believe), it says he's part of Arzest.
I'm really curious what Arzest is up to, and slightly concerned about the lack of news. Their last (and only) major game was Yoshi, since then they made Boost Beast, a mobile game, and also lent Manabu Kusunoki and Naoto Ohshima to design characters in Terra Battle (Arzest mentions Terra Battle in their work list).
I hope Nintendo work very closely with Arzest on a major non-Yoshi game, a new IP preferably. And if I had it my way; it'd be Sonic! Don't forget, Arzest and Artoon before it, were formed by a lot of veterans from Sonic Adventure 1 and earlier games like Panzer Dragoon and such.
This team gets so much flak for their Yoshi games, but honestly, it's impossible to be on par with the original if you don't get the original team on it, and also for YNI the music (which was by Chamy Ishii of T's Music by the way) is what was the real sour note (HA) of the game. Also the character models were by Imageepoch of all teams.
You know what kind of games they should make with Yoshi? More like Topsy-Turvy, that thing is crazy-looking and inventive, that's the true Arzest spirit carried over from Sega, they dared to be creative and different, just like Nintendo. Don't put them on "me too" projects trying to emulate a previous Nintendo game, especially at such a high bar as Yoshi's Island.
Get them on a new IP, preferably an original 3D platformer, make that their "Yooka-Laylee" of Sonic Adventure. I mean Ohshima has a furball ready for the job!