Via Rambling Rican we know some of the people who will be appearing at SASUKE 21. She posted about that here, here, and here.
The list so far is:
The G4 team of this SASUKE's ANC winners:
Brian Orosco ブライアン・オロスコ
plus Levi "Hits" Meeuwenberg (speaking of nicknames, what's with the Wiki adding in the nicknames of Brian, Levi and Luci? They're supposed to be "Ninja Warriors" not "American Gladiators." Can you imagine if everyone on SASUKE had American Gladiator nicknames?). リーヴァイ・ミューエンバーグ
Also the Attack of the Show hosts Olivia Munn and Kevin Pereira.
(Edit: For those who didn't get the joke, I gave the following people American Gladiator-style nicknames and then just kind of gave up part-way through.)
The SASUKE All-Stars:
Makoto "Captain" Nagano 長野誠,
Shingo "Gas" Yamamoto 山本進悟,
Bunpei "Slim" Shiratori 白鳥文平,
Toshihiro "Flame" Takeda 竹田敏浩
and Mr. SASUKE Katsumi "Sucky" Yamada 山田勝己.
Daisuke "Balls" Miyazaki 宮﨑大輔 and his teammates
Katsuyuki "Who" Urawa 浦和克行
Sho "Are" Iwanaga 岩永生
Masakatsu "You" Izuma 猪妻正活
Naoki "Air" Iketani 池谷直樹
Daisuke "Spring" Nakata 中田大輔
Masaki "Pops" Nomura 野村将希
Kenjirou "Gramps" Ishimaru 石丸謙二郎
Hiromichi "Smiley" Sato 佐藤弘道
Hiroshi "Gloves" Yamamoto of ロバート 山本博
Dante "Dante" ダンテ
Passion "Passion" Yara パッション屋良
Mitusomi "This is too taxing" Takahashi 高橋光臣
Also non-famous people via SASUKE Maniac or some other way
Yuuji Urushihara 漆原裕治
Yamanaka Kazuo 山中和男
Koji Ida 井田浩二
Shunzou Kikuchi 菊池俊三
Takuya Miyagi (Mr. SASUKE's assassin) 宮城拓也
Tomohiro Kawaguchi 川口朋広
Ryo Matachi 又地諒
Kazuma Asa 朝一眞
Jun Satou 佐藤惇
Akinori Murakami 村上明範
Koji Hashimoto 橋本亘司
Takayuki Kubota 久保田崇之
Some digging has also found that the following people are going to be there too:
Former J-Leaguer and now free announcer (meaning he's not connected to a TV station not that he works for free) 波立紀夫 Norio Haryu. He's been in several of the past SASUKEs but he keeps getting the digest treatment.
Some dancer dude named Ke Maeda 前田けゑ.
Comedy ladies Moeyan モエヤン (remember them from the race around Tokyo on SASUKE Maniac?)
Keitaro Katayama 片山敬太郎 from the Muscle Musical will be there.
Model/talent Ryo Shirai 白井涼 will also be there.
Also, one of your announcers will be Yuriko Takahata 高畑百合子.
And, HEY, if you live in Aichi, Gifu or Mie prefectures, enjoy the Dragons vs. Tigers game on CBC that you'll have to wait to end before you can enjoy SASUKE.
More news when it comes!