Harshax: Is this being produced by Sega? Because if so it will indeed be a Steam exclusive.
NO! Kickstarter campaign. So fund, let the man know that you would like to see it here and point the other japanese games that came on GOG lately.
Sega gave the rights back to the Shenmue creator (though i doubt that was for free or because they are such nice guys)
"If this project reaches its funding goal, Shenmue 3 will be available on the PS4 and PC. "
As for why the Kickstarter...I really doubt that Sony handed them the needed funds or any funds at all. So far this is heading towards one of the most succesful KS campaigns ever.
The PS4 exclusivity might be because XBox was always only a small fraction of the japanese market and had trouble to penetrate it. So, if he wants the game to sell in Japan, that was a good move, as he's gonna reach as many customers as he wants. The japanese devs were always reluctant to release their games on western platforms. We are lucky that he boarded the PC trend that is going now on the japanese market and in West.