Suda 51 stated in the past that NMH2 is the last game for the Wii, what he didn't say was where he expected a sequel would land if there was ever to be one...until now.
From a Game Informer Interview:
Seems like he really enjoys the series, I loved NMH2 though it got a bit "been there done that" by the end but still I love the game, style and humour.
Source
From a Game Informer Interview:
QUOTE said:GI: You've made comments about the No More Heroes series continuing on a new platform. Do you expect to make a No More Heroes 3? And do you think No More Heroes 2 might eventually be rereleased on Xbox 360 like the original in Japan?
Suda51: If there is a chance to continue No More Heroes, I am interested in making NMH3. I personally think that NMH is a game for Wii, so I would be very happy if I could make a game for the Wii’s successor, whenever that might be. I was not involved in the production of the 360 version of NMH1, so I don’t know anything about that.
Seems like he really enjoys the series, I loved NMH2 though it got a bit "been there done that" by the end but still I love the game, style and humour.
Source