Prediction: PS5 and Xbox Series X combined will sell less than 120M.

[UnderwaterFunktown]

I don't see it.
Even if the sales trajectory starts looking that rough, I think both Sony and Microsoft would be willing to bite the bullet and cut prices significantly, which should save them from ending up quite that low. But I don't think that will be necesarry in the first place. I could see them selling slower than the current gen, but I also wouldn't be suprised if the next gen ends up being a bit longer, so I don't expect lifetime sales to be too different.