upcoming debut
It has been confirmed that Jin Kazama will indeed be in the upcoming Tekken 6. I, personally, have seen two Tekken 6 promotional videos featuring Jin. One is of him fighting against Lili. Then, after some time, Hwoarang breaks through a stained glass window while riding his motorcycle.

The other video is of Jin performing a kata of some sort. The image quality is amazing. Sweat droplets, pores, as well as other markings on the skin are detailed.

Only one of the two outfits he wears in these videos appears to be new, which is a black tank top with a pair of black pants. As mentioned before, the other outfit is not new, it is the same as his default costume in Tekken 5.

Here are some screen captures of Tekken 6 (all of which include Jin).
1 / 2 / 3 / 4 / 5 / 6