I missed out on the Yakuza games for years but I feel like this is the perfect time to get into them as all of the remaining Yakuza games will be making their way to the PS4.
In the most recent issue of Famitsu, Sega has announced that remastered versions of Yakuza 3, 4 and 5 are going to be released on PS4 in the next 12 months. These remasters will of course include updated visuals and frame rates. Yakuza 0, and Yakuza Kiwami, the remake of the first game, are currently available for the PS4 as is Yakuza 6: The Song of Life. Yakuza Kiwami 2 is coming later this Summer so this move makes complete sense for those who want to experience the entire series and it's nice that the whole series will be available on the PS4.
Yakuza 3 is planned to be released in Japan this Summer, Yakuza 4 in Fall of 2018 and Yakuza 5 in Spring of 2019. It should be noted that only Japanese release dates have been announced, but given the fact that the four games in the series have been released in North America in the last two years, I'm sure we will get these games sooner rather than later.