I've written about this elsewhere, but this is really a prime localization opportunity for Sega.
-releasing a prequel avoids rebooting the franchise, creating split mythologies and fanbases
-gives Sega an opportunity for a fresh start with the games - fresh start for their branding of Yakuza in the West, their messaging, etc.
-if this game is at least moderately successful in the West, then Sega has somewhat low risk options ahead of them as far as continuing the Yakuza momentum because they can just release HD compilations of 1+2 and 3+4 to catch the new fans up to speed. Unfortunately this kinda screws over the old fans if in the meantime there's nothing new for them to play, and it's hard to add on to Yakuza games since they are already full of side content. So uh...make like, Yakuza cooking sims or something, or localize Ishin =3
Of course, Yakuza games are still risky what with the licensing and the relatively dense script but they can make this work dammit!