I don't know if anyone would be interested in this, seeing as this is hardly concrete information, but seeing as we're lacking sales numbers, I was curious to see how the popularity of Yakuza fared against other games so here are some order "sizes" for games from the shop I get my games from. They like to post their stock, so its good indication for me, I wouldn't take any of this as gospel, but I think Kiwami is doing well in Malaysia at the very least. This will probably be pretty different to the US, but I think Kiwami has a chance to do just as well as Zero given its lower price point.
Yakuza 0 (first picture, preorders, second picture, restock after two weeks) - Preorders obviously look low, I think at the time, most places sold out and they couldn't fill demand because of the good word of mouth. The restock shows more copies, but still not very many.
Yakuza Kiwami (first picture, steelbook, second picture, regular edition) - The steelbook here is the R1 version @ RM149 (US$35), and the R3 standard at RM99 (US$23). The steelbook was available for preorder 1 month before, so it could be why there are so many more steelbooks. A $12 difference might not sound very much to US folk, but a 50% price difference and RM50 difference is a lot so I'm actually very surprised people didn't switch over to the standard version.
Either way, Zero's good word of mouth has probably helped Kiwami sell more copies over here at least. Hopefully this means retailers can be more bullish about the series prospects and that they can spend more on marketing it. This shop was quite active in promoting Kiwami preorders.
Here's how Yakuza compares to other games preorders.
Utawarerumono: Mast of Truth (the new one) (1st order),
Uncharted Lost Legacy (1st order),
Persona 5 (1st order),
Persona 5 (restock after two weeks)