Its possible as the sales are not far off, but I cannot imagine too many people who want a Playstation buying it over the PS5. If someone wanted to go cheap for a next gen console in the meantime, they are more likely to just get a Series S and get a PS5 when they can get one so their first investment wouldn't be a waste (it is certainly cheap enough for people to jump on).
Speaking of Series S, that may very well be why Sony is doing this. The SS is easier to produce, and hence why it is more available and selling so well. The PS5 digital and Disc versions are pretty much the same, both more expensive than the Series S and hard to find. This could be their solution to tap into the market of people looking to buy cheap till the PS5 becomes more available. Their next big three games are cross gen afterall (Horizon, GoT, Gran Turismo).
A million PS4's worldwide in the year isn't much, you have general replacement sales combined with those that buy it for the library just like all those who were doing the same 5 or 6 years after launch.
Research shows Video games help make you smarter, so why am I an idiot