We are going to have a PS4 at 21M and a Switch at 18M for the fiscal year.
Not possible for PS4 I'm afraid. It's definitely going to be down from last year. 18.5m sell-through is my prediction for the calendar year, probably pretty similar for fiscal.
I predicted 18m for Switch, 18.5m for PS4 since about April. Though with the PS4 having a lead of 2.8m for 2018 so far the amount the Switch is going to have to beat the PS4 by over the holidays keep increasing.
I'm confidant the Switch will have a better November+December combined, but I'm not sure it's going to beat the PS4 in those months by more than a maximum of 2m, even that might be pushing it.