That particular part of a traditional samurai armor is called the Haidate. I've been seeing Kimonos around and am also interested in the prospect (however infinitesimally remote) of developing a Japanese set of armor. The Haidate cover the upper thigh and knee and not the abdomen (and are a form of lamellar armor). However, to fit with the existing armor system you may have to use a tasset platform to allow for the Suneate (which cover the shin and knee).