Just read from GA forum that the game is not on System 246, Chihiro nor Tri-Force.
Ripped from Rubeus post in his thread
http://www.the-magicbox.com/gaming.htm
Japanese Arcadia magazine reported that Namco's new arcade fighting game Tekken 5 will run on a new arcade board, which is not one of the console friendly board System 246, Chihiro or Triforce. Other tidbits of Tekken 5
* Tekken 5 will have an infinite battle arena with no boundaries like in Tekken 1-3.
* Raven is a ninja who controls ninjutsu
* Asuka Kazama is the cousin of Jin
* Feng Wei uses martial art to battle, but fighting style is similar to Paul
* The Wall / Obstacle system is improved to make the game more interesting
* Some levels will have destructible objects
* Kuma / Panda are once again time release characters
* Position change function in Tekken 4 is removed, so left/right throws are possible again
* Juggles are possible like in Tekken Tag Tournament
* Low Parry Maneuver are revised
* There are pitfalls in certain arenas, such as laser beams and fire
* There will be a Beginner Mode and a Conquest Mode similar to Soul Calibur 2