I don't know if I see 400k happening honestly. Powerful Pro 2016 did a bit less than 500k when the PSV wasn't completely dead and the PS3 version was present. I can see the PS4 version going up from the last one, but even that isn't a certainty when we've had so many underperformers on the system lately (many of them family oriented). I don't think the PSV version will do much at all this time around, so the PS4 will have to carry the weight.
JPPY 2016 had the 16th best FW and 15th best LTD of any PS4 SKU released at the time, according to the GameDataLibrary, at 75.505 and 203.892.
Hardware
At the time of JPPY 2016's release, PS4's LTD was 2.777.073 and its YTD was 475.993. That was when the PS4 was on market for 114 weeks. That's 19.285 units per week on average from week 1-114.
Right now, the PS4's LTD is 6.401.139 and its YTD is 508.736 already (thanks to MHW ofc). We're at week 207 for the PS4 right now. That's 38.968 units per week on average from week 115-207. That's double!
Software
It's a shame that we don't have CY 2017 numbers yet. From CY 2015 to CY 2016, we have a PS4+PSV software sales increase with 30,8% from 10.320.207 to 13.496.599 (5.114.598 + 5.205.609 to 8.672.086 + 4.823.793). While the PSV declined very hard in 2017, I think the PS4 can make up for the PSV's share loss in 2017, considering the strong line-up of software (both multiplatform and exclusive).
So I think the position of the PS4+PSV combo is at least as good and maybe even better than in the Spring of 2016. We see a lot of hardcore exclusives struggle, but JPPY is a sports title, so it might appeal to more casual fans as well. The series has historically performed strongly. JPPY 2018 installment must sell 142.166 copies sold FW and 404.344 copies sold LTD in order to stay flat compared to JPPY 2016 on the same platforms. With the exception of JPPY 2014 (which was released when the PS4 was out for 8 months, but not on PS4), every installment since JPPY 2010 has been able to sell at least 300k copies across its two best-selling SKUs. So I think it'll be fine.
I think a Switch version for this specific game would prevent it from seeing a substantial collapse. Maybe Konami will add it later, but I'm kind of surprised it's not releasing day and date with the other versions after the huge success of Bomberman.
Bomberman and JPPY are very different games, but I still agree on this. There's a gap that Konami could fill with JPPY 2018 on the Switch. They better make sure they're on it earlier than Bandai Namco tho.