Do you think the PS4 and Xbox One could sell another 17 million units lifetime? And yes the pandemic has helped boost sales of video games across the board.
Sony shipped 13.6 million PS4's from April 2019 to March 2020. Even if PS4 shipment figures drop by 50% per year that is 6.8 million for the current fiscal year, 3.4 million for the next, 1.7 million, and 0.85 million for a total of 12.75 million. Even with the PS5 coming out this holiday, I don't see PS4 shipment figures dropping by 50%.
It actually all depends on how much will PS4/XB1 be available on the market and how the release of next gen consoles will affect the sales of current gen consoles. But it will definitely be very close to what PS3/360 did. So, I would say that PS4/XB1 will sell around the same within a 1-2 million margin of error in any side.